Set up read the docs integration, update docs readme.

[merrygoat]

Heh, so I am dumb. We can't actually do this until the project goes public. Relatively easy to do then anyway.

[rhysgt]

This is public now, so we can look to get readthedocs integration, and to develop the documentation some more

[rhysgt]

I've used GitHub Pages to accomplish this, so when we next push develop -> master, we should have a page at mechmicroman.github.io/defdap.

[merrygoat]

That's great. As I see it, that is equivalent to read the docs. If anything slightly superior since it is all in the same github ecosystem.