First version of Read the Docs

`Sphinx` package gets installed when running `pip install requirements/dev.txt` as part of the dev bundle (imported from playdoh / funfactory). This is part of playdoh. Since Sphinx is already there, I suggest that sphinx_rtd_theme gets also there as well as everything else you need to do development (either code or docs).

[0] https://github.com/mozilla/oneanddone/blob/master/requirements/dev.txt
[1] https://github.com/mozilla/funfactory/blob/master/funfactory/requirements/dev.txt#L8