Add docs badge to README

I just added the badge you requested to your README: ![Inline docs](http://inch-pages.github.io/github/futhr/spree-unifaun.png)

Your status page for this project is http://inch-pages.github.io/github/futhr/spree-unifaun

If you have any questions/suggestions, feel free to post them here or create an issue in the Inch Pages project. Thanks for giving this a shot!