Add link to compatibility project

@dhh I know you asked me to make a compatibility file, but I thought doing that would introduce a slew of pull requests and issues that aren't relevant to Turbolinks itself.  I figured it'd be better off as it's own project, so I built this Github Pages site:

http://reednj77.github.com/turbolinks-compatibility

I'm open to suggestions for improvements.

This PR just adds a link to it in the readme.