adds plugins command to print out info about CocoaPods plugins

Originally in reference to #1926

Took longer than just the train ride home. :)

@orta, this is currently pointed to my yetanotherbucket bucket on S3. Probably want to change that to an actual cocoapods web asset. Is there something I can point it to? 

![selfie-2](http://i.imgur.com/zoue98e.png)