docs(README): add a Bitdeli badge

Closes #1605

Author: bitdeli-chef

README.md

@@ -2,7 +2,9 @@
 
 ***
 
-[![Build Status](https://secure.travis-ci.org/angular-ui/bootstrap.png)](http://travis-ci.org/angular-ui/bootstrap) [![devDependency Status](https://david-dm.org/angular-ui/bootstrap/dev-status.png?branch=master)](https://david-dm.org/angular-ui/bootstrap#info=devDependencies)
+[![Build Status](https://secure.travis-ci.org/angular-ui/bootstrap.png)](http://travis-ci.org/angular-ui/bootstrap)
+[![devDependency Status](https://david-dm.org/angular-ui/bootstrap/dev-status.png?branch=master)](https://david-dm.org/angular-ui/bootstrap#info=devDependencies)
+[![Bitdeli Badge](https://d2weczhvl823v0.cloudfront.net/angular-ui/bootstrap/trend.png)](https://bitdeli.com/free "Bitdeli Badge")
 
 ## Demo