docs: add libsasl as system requirement on linux (#1257)

* docs: add libsasl as system requirement on linux

* docs: add openldap as system dependencies on linux too

Fix #1256

docs/installation.rst

@@ -24,13 +24,13 @@ Here's how to install them:
 For **Debian** and **Ubuntu**, the following command will ensure that
 the required dependencies are installed: ::
 
-    sudo apt-get install build-essential libssl-dev libffi-dev python-dev python-pip
+    sudo apt-get install build-essential libssl-dev libffi-dev python-dev python-pip libsasl2-dev libldap2-dev
 
 For **Fedora** and **RHEL-derivatives**, the following command will ensure
 that the required dependencies are installed: ::
 
     sudo yum upgrade python-setuptools
-    sudo yum install gcc libffi-devel python-devel python-pip python-wheel openssl-devel
+    sudo yum install gcc libffi-devel python-devel python-pip python-wheel openssl-devel libsasl2-devel openldap-devel
 
 **OSX**, system python is not recommended. brew's python also ships with pip  ::