add pledgie button

README.md

@@ -11,6 +11,11 @@ reveal.js comes with a broad range of features including [nested slides](https:/
 - [Browser Support](https://github.com/hakimel/reveal.js/wiki/Changelog): Explanation of browser support and fallbacks.
 
 
+The framework is and will remain free. Donations are available as an optional way of supporting the project.
+
+[![Click here to lend your support to: reveal.js and make a donation at www.pledgie.com !](http://www.pledgie.com/campaigns/18182.png?skin_name=chrome)](http://www.pledgie.com/campaigns/18182)
+
+
 ## Instructions
 
 ### Markup