Link to Government Showcase, fixes #293

This adds a link to the Government showcases re #293 

What do you think about the copy? Should 'App' be used at all? Should 'Government __ Showcase' be lowercase?

![screen shot 2014-07-29 at 12 45 15 pm](https://cloud.githubusercontent.com/assets/1305617/3740802/54d152cc-1759-11e4-9586-4b59a06fc342.png)