Setup docs

[mmcky]

The docs should be setup in docs and use sphinx to build

• [x] a section on the defaults used and structure of the repository
• [x] a section on how to customise using conf.py
• [x] links to upstream sphinx docs

[mmcky]

@AakashGfude once we get a demo version going can you jupinx-quickstart a docs directory :-)

[mmcky]

• [x] setup readthedocs and use rtd theme for html production.