create a readthedocs page

[jeremymanning]

Good suggestion from one of our SoftwareX reviewers:

I suggest creating a documentation website using an option like Sphinx and ReadTheDocs.org, which provides free hosting, or using a wiki on GitHub. The Sphinx + RTD option is nicer and more flexible, but takes more setup. In either case, the main benefit would be having separate pages that could split out things like user guide, FAQ, implementation details, and grammar specifications. For the README file, I suggest just having a brief introduction and a quick example of using Davos to get people started, with those two things taking up a about a page. A link to an FAQ section can still be included to refer skeptical readers, but I think the pitch in the README can be very simple and focused on the benefits of Davos, rather than trying to contrast with all the other available systems. The quick start section can show simple examples to help play up a strength of Davos, which is that most users will need to read very little documentation to get started.