python/docs cleanup

Honestly, this pull request as much about me getting familiar with Github workflows as it is about the project, but here are a few small changes I made, mostly with the intent of having the repo in better condition for someone first checking it out.

1. Updated python/docs/README.md file to list required packages (sphinx, sphinx_rtd_theme, numpydocs).
2. Removed and gitignored python/docs/_build, which the developer should rebuild to match current source.
3. Removed and gitignored *pyc files.