Update README.md

Author: rmariuzzo

README.md

@@ -3,6 +3,7 @@
 > A jQuery plugin that give you nice powers over your checkboxes. http://rmariuzzo.github.io/checkboxes.js
 
 [![Build Status](https://travis-ci.org/rmariuzzo/checkboxes.js.svg?branch=develop)](https://travis-ci.org/rmariuzzo/checkboxes.js)
+[![Built with Grunt](https://cdn.gruntjs.com/builtwith.png)](http://gruntjs.com/)
 
 ## Installation