Add basic documentation

[macro1]

Some basic documentation should be added which can be published in a readable way. Possibly with 'Read the Docs' or something similar, since that is popular with many libraries.

Detail isn't important for this. Just a clean base so more documentation sections can be added later.

[willingc]

@macro1 I'm happy to mentor/pair with someone interested in using RestructuredText, Sphinx, and Read the Docs.

[davidfischer]

To start on this one, I think we just need some more details in the README. If that goes well, we can expand to a full docs/ directory and Read the Docs. To start, we need sections on:

• What the repository is about
• Contributing to the site
  • Setting up the dev environment, running tests, etc.
  • Issues to work on, etc.
• Where the site lives (eg. pythonsd.org)
• How to use the site for your own meetup!
• Deploying the site