create a documentation site
the readme is nice, but it's getting too long and may be hard to parse for new users. having a more readable docs site may be better. this came out of the usability review (#11).
- build with mkdocs locally
- create rtfd branch to render on rtfd.org
- make the render work (fails for now)
- automatically link to the right build numbers in the docs
- make a splash page and simpler step-by-step instructions