packaging/doc: support installing the encryption libraries as a extra…

… and recommend it in the docs

[skip ci]

README.rst

@@ -67,7 +67,8 @@ Requirements and Tested Platforms
 - Python: 
 
  - 3.5-3.7
- - tinyaes_ 1.0+ (only if using bytecode encryption)
+ - tinyaes_ 1.0+ (only if using bytecode encryption).
+   Instead of installing tinyaes, ``pip install pyinstaller[encryption]`` instead.
 
 - Windows (32bit/64bit):
 

doc/usage.rst

@@ -203,12 +203,16 @@ To encrypt the Python bytecode modules stored in the bundle,
 pass the ``--key=``\ *key-string*  argument on
 the command line.
 
-For this to work, you must have the tinyaes_
-module installed.
+For this to work, you need to run::
+
+    pip install pyinstaller[encryption]
+
 The *key-string* is a string of 16 characters which is used to
 encrypt each file of Python byte-code before it is stored in
 the archive inside the executable file.
 
+This feature uses the tinyaes_ module internally for the encryption.
+
 
 .. _defining the extraction location:
 

setup.cfg

@@ -67,6 +67,8 @@ hook_testing =
     pytest >= 2.7.3
     execnet >= 1.5.0
     psutil
+encryption =
+    tinyaes>=1.0.0
 
 [options.package_data]
 # This includes precompiled bootloaders and icons for bootloaders