Add basic docs

[jettify]

We should have at least one page docs, with basic examples.

[Olegt0rr]

@jettify, what kind of docs recommened for aio-libs?

[Dreamsorcerer]

You probably won't get a reply. But, if you want to follow this up, look at the other repositories such as aiohttp-jinja2 and try to setup a similar Sphinx build.

Probably want a usage/tutorial section, which could probably be a more detailed version of the README example. Then an API/reference section which documents the actual functions/methods and their parameters.