Write basic docs

[thoward]

Include, at minimum:

• some usage examples
• a description of what RST features are covered, and what the expected output will be (e.g. what kind of tag, and what CSS class)
• a description of what RST features are NOT covered, and how those are output/handled
• explain the relationship to the parser project, and which things are handled by parser, but not by renderer, vs things just not handled by parser at all
• add a "contributing" section, including basic dev docs on how to make changes, run tests, publish new version of the package, etc.

[Tythos]

I wouldn't mind adding some docs, especially since there are some other features I'd love to add support for and should probably make sure they're written up before I submit a PR. What level of detail and organization did you have in mind? An extended README? Full docs folder? JSDoc generation?

[Tythos]

UPDATE: See PR #10