add gittip

Author: DennisOSRM

index.html

@@ -20,6 +20,7 @@
 <hr>
 Try our amazing public routing service at <a href="http://map.project-osrm.org/">http://map.project-osrm.org/</a> or follow us on <a href="https://twitter.com/#!/ProjectOSRM">Twitter</a>.
 <p>
+<iframe style="border: 0; margin: 0; padding: 0;" src="https://www.gittip.com/DennisOSRM/widget.html" width="48pt" height="22pt"></iframe>
 <A NAME="buildstatus"><h2>Current build status:</h2></A>
 <table>
   <thead>