[docs] [issue22394] Update documentation building to use venv and pip

Brett Cannon added the comment: I'm going to at least update the Makefile to have a ``make venv`` that will do the steps necessary to create a venv and then check out the necessary tools. It should also be set up so that running the command with a pre-existing venv will update it. This should all lead to commands like ``make html PYTHON=venv/bin/python3`` to work. ---------- assignee: docs@python -> brett.cannon _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22394> _______________________________________