refactor virtualenv docs

[qwcode]

use the Standard Pypa Docs Template

[qwcode]

@Ivoz, just a thought, but you might be interested in taking this issue.
I'm doing similar for pip and setuptools at the moment.

[qwcode]

closing as a PUG issue, but instead will mention in the "Work in Progress" section
https://python-packaging-user-guide.readthedocs.org/en/latest/future.html#work-in-progress

[Ivoz]

Reminds me, need to get back on to polishing my pull.