add sphinx docs

[brooksandrew]

reference for adding to readthedocs
https://docs.readthedocs.io/en/latest/getting_started.html#

sphinx tutorial:
https://media.readthedocs.org/pdf/brandons-sphinx-tutorial/latest/brandons-sphinx-tutorial.pdf

Publishing sphinx-generated docs on github
https://daler.github.io/sphinxdoc-test/includeme.html