Update README.md

Author: PhilJay

README.md

@@ -26,6 +26,8 @@ Gittip
   <img alt="Support via Gittip" src="https://rawgithub.com/twolfson/gittip-badge/0.2.0/dist/gittip.png"/>
 </a>
 
+[![Gratipay](http://img.shields.io/gratipay/PhilJay.svg)](https://gratipay.com/PhilJay)
+
 Demo
 -----