Add readme with notice about development status.

I notice you guys didn't have a readme yet, so I just made this one for you quickly.

I added the development status, because the amazing [Producing OSS](http://producingoss.com/) taught me that you should always [be explicit about the development status](http://producingoss.com/en/getting-started.html#development-status) of a project.

Thanks again guys. This is going to help a lot as I forge ahead on my own build in the next 2 weeks.