Document new libkrb5-dev system dependency for pykerberos

[pdecat]

This PR documents the new libkrb5-dev system dependency introduced by #144 for pykerberos .

On Ubuntu, without libkrb5-dev, installation fails with:

# rm -rf .venv
# python3 -m venv .venv
# ./.venv/bin/pip install --no-cache-dir aws-adfs==1.21.0
Collecting aws-adfs==1.21.0
  Downloading https://files.pythonhosted.org/packages/7f/7b/d1f893d8f523137a412ffc86b82b6709fd03904f000358b2e6c6e121ad7e/aws-adfs-1.21.0.tar.gz (52kB)
    100% |████████████████████████████████| 61kB 993kB/s
Collecting boto3>=1.9.6 (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/39/8b/250778bc5fd4b9a91d7916f8729b346931be419052130548617139247ba6/boto3-1.10.41-py2.py3-none-any.whl (128kB)
    100% |████████████████████████████████| 133kB 1.3MB/s
Collecting botocore>=1.12.6 (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/49/e0/a9a53656126a635120c0f7eaee3ff3b26a4a08596d10e7192fd91ce19e5c/botocore-1.13.41-py2.py3-none-any.whl (5.8MB)
    100% |████████████████████████████████| 5.8MB 1.5MB/s
Collecting click (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/fa/37/45185cb5abbc30d7257104c434fe0b07e5a195a6847506c074527aa599ec/Click-7.0-py2.py3-none-any.whl (81kB)
    100% |████████████████████████████████| 81kB 218kB/s
Collecting configparser (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/7a/2a/95ed0501cf5d8709490b1d3a3f9b5cf340da6c433f896bbe9ce08dbe6785/configparser-4.0.2-py2.py3-none-any.whl
Collecting fido2<0.9.0,>=0.8.1 (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/97/03/9ce85396423a4b9897cc3295a605b63dffd06940e65c1cccd51c2c016864/fido2-0.8.1.tar.gz (201kB)
    100% |████████████████████████████████| 204kB 1.5MB/s
Collecting requests[security] (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/51/bd/23c926cd341ea6b7dd0b2a00aba99ae0f828be89d72b2190f27c11d4b7fb/requests-2.22.0-py2.py3-none-any.whl (57kB)
    100% |████████████████████████████████| 61kB 1.4MB/s
Collecting requests_kerberos (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/ee/a2/866f2b9a60f75055137b9ad127033e397963b2c4769d4b5fab1c3c7e8be3/requests_kerberos-0.12.0-py2.py3-none-any.whl
Collecting lxml (from aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/95/60/552fc6e027bc1158ba4691cccfdf6eb77f206f2f21d3c1c5f23b89f68a0e/lxml-4.4.2-cp37-cp37m-manylinux1_x86_64.whl (5.7MB)
    100% |████████████████████████████████| 5.8MB 1.4MB/s
Collecting jmespath<1.0.0,>=0.7.1 (from boto3>=1.9.6->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/83/94/7179c3832a6d45b266ddb2aac329e101367fbdb11f425f13771d27f225bb/jmespath-0.9.4-py2.py3-none-any.whl
Collecting s3transfer<0.3.0,>=0.2.0 (from boto3>=1.9.6->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/16/8a/1fc3dba0c4923c2a76e1ff0d52b305c44606da63f718d14d3231e21c51b0/s3transfer-0.2.1-py2.py3-none-any.whl (70kB)
    100% |████████████████████████████████| 71kB 225kB/s
Collecting urllib3<1.26,>=1.20; python_version >= "3.4" (from botocore>=1.12.6->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/b4/40/a9837291310ee1ccc242ceb6ebfd9eb21539649f193a7c8c86ba15b98539/urllib3-1.25.7-py2.py3-none-any.whl (125kB)
    100% |████████████████████████████████| 133kB 1.4MB/s
Collecting python-dateutil<2.8.1,>=2.1; python_version >= "2.7" (from botocore>=1.12.6->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/41/17/c62faccbfbd163c7f57f3844689e3a78bae1f403648a6afb1d0866d87fbb/python_dateutil-2.8.0-py2.py3-none-any.whl (226kB)
    100% |████████████████████████████████| 235kB 1.6MB/s
Collecting docutils<0.16,>=0.10 (from botocore>=1.12.6->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/22/cd/a6aa959dca619918ccb55023b4cb151949c64d4d5d55b3f4ffd7eee0c6e8/docutils-0.15.2-py3-none-any.whl (547kB)
    100% |████████████████████████████████| 552kB 1.4MB/s
Collecting cryptography>=1.5 (from fido2<0.9.0,>=0.8.1->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/45/73/d18a8884de8bffdcda475728008b5b13be7fbef40a2acc81a0d5d524175d/cryptography-2.8-cp34-abi3-manylinux1_x86_64.whl (2.3MB)
    100% |████████████████████████████████| 2.3MB 1.5MB/s
Collecting six (from fido2<0.9.0,>=0.8.1->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/65/26/32b8464df2a97e6dd1b656ed26b2c194606c16fe163c695a992b36c11cdf/six-1.13.0-py2.py3-none-any.whl
Collecting chardet<3.1.0,>=3.0.2 (from requests[security]->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/bc/a9/01ffebfb562e4274b6487b4bb1ddec7ca55ec7510b22e4c51f14098443b8/chardet-3.0.4-py2.py3-none-any.whl (133kB)
    100% |████████████████████████████████| 143kB 1.5MB/s
Collecting certifi>=2017.4.17 (from requests[security]->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/b9/63/df50cac98ea0d5b006c55a399c3bf1db9da7b5a24de7890bc9cfd5dd9e99/certifi-2019.11.28-py2.py3-none-any.whl (156kB)
    100% |████████████████████████████████| 163kB 1.4MB/s
Collecting idna<2.9,>=2.5 (from requests[security]->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/14/2c/cd551d81dbe15200be1cf41cd03869a46fe7226e7450af7a6545bfc474c9/idna-2.8-py2.py3-none-any.whl (58kB)
    100% |████████████████████████████████| 61kB 1.3MB/s
Collecting pyOpenSSL>=0.14; extra == "security" (from requests[security]->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/9e/de/f8342b68fa9e981d348039954657bdf681b2ab93de27443be51865ffa310/pyOpenSSL-19.1.0-py2.py3-none-any.whl (53kB)
    100% |████████████████████████████████| 61kB 1.5MB/s
Collecting pykerberos<2.0.0,>=1.1.8; sys_platform != "win32" (from requests_kerberos->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/9a/b8/1ec56b6fa8a2e2a81420bd3d90e70b59fc83f6b857fb2c2c37accddc8be3/pykerberos-1.2.1.tar.gz
Collecting cffi!=1.11.3,>=1.8 (from cryptography>=1.5->fido2<0.9.0,>=0.8.1->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/16/cd/1f4ddf6be8300713c676bb9f3a2d3b8eb8accc0a6a24f57d4f6c4cd59d34/cffi-1.13.2-cp37-cp37m-manylinux1_x86_64.whl (398kB)
    100% |████████████████████████████████| 399kB 1.4MB/s
Collecting pycparser (from cffi!=1.11.3,>=1.8->cryptography>=1.5->fido2<0.9.0,>=0.8.1->aws-adfs==1.21.0)
  Downloading https://files.pythonhosted.org/packages/68/9e/49196946aee219aead1290e00d1e7fdeab8567783e83e1b9ab5585e6206a/pycparser-2.19.tar.gz (158kB)
    100% |████████████████████████████████| 163kB 1.4MB/s
Installing collected packages: urllib3, jmespath, six, python-dateutil, docutils, botocore, s3transfer, boto3, click, configparser, pycparser, cffi, cryptography, fido2, chardet, certif
i, idna, pyOpenSSL, requests, pykerberos, requests-kerberos, lxml, aws-adfs
  Running setup.py install for pycparser ... done
  Running setup.py install for fido2 ... done
  Running setup.py install for pykerberos ... error
    Complete output from command /home/patrick/workspaces/aws/aws-adfs/.venv/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-qwopu5lw/pykerberos/setup.py';f=ge
tattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-record-cazi4npz/install-record.txt
 --single-version-externally-managed --compile --install-headers /home/patrick/workspaces/aws/aws-adfs/.venv/include/site/python3.7/pykerberos:
    running install
    running build
    running build_ext
    building 'kerberos' extension
    creating build
    creating build/temp.linux-x86_64-3.7
    creating build/temp.linux-x86_64-3.7/src
    x86_64-linux-gnu-gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O2 -Wall -g -fstack-protector-strong -Wformat -Werror=format-security -g -fwrapv -O2 -g -fstack-
protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/home/patrick/workspaces/aws/aws-adfs/.venv/include -I/usr/include/python3.7m -c src/kerberos.c
 -o build/temp.linux-x86_64-3.7/src/kerberos.o
    In file included from src/kerberos.c:19:
    src/kerberosbasic.h:17:10: fatal error: gssapi/gssapi.h: No such file or directory
       17 | #include <gssapi/gssapi.h>
          |          ^~~~~~~~~~~~~~~~~
    compilation terminated.
    error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

    ----------------------------------------
Command "/home/patrick/workspaces/aws/aws-adfs/.venv/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-qwopu5lw/pykerberos/setup.py';f=getattr(tokenize, 'open',
open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-record-cazi4npz/install-record.txt --single-version-extern
ally-managed --compile --install-headers /home/patrick/workspaces/aws/aws-adfs/.venv/include/site/python3.7/pykerberos" failed with error code 1 in /tmp/pip-install-qwopu5lw/pykerberos/

[venth]

Released with version: 1.21.1

[venth]

Thanks 👍