Message 201435 - Python tracker

Draft docs patch attached. This splits out a new "Software Packaging and Distribution" section in the main docs index, with distutils, ensurepip and venv as the specific entries.

There's a couple of questions I need answered regarding the behaviour of pip in order to document --user properly:

* how does pip install react when --user is passed while a virtual environment is active?
* how does pip install react when both --root and --user are passed?