Update index.html

Author: debugger22

app/index.html

@@ -88,7 +88,8 @@ <h4>About</h4>
       <div class="footer-left-text-block">
         this project is open source, you can view it on <a href="https://github.com/debugger22/github-audio" target="_blank">GitHub</a><br/>
         developed by <a href="https://github.com/debugger22" target="_blank">@debugger22</a><br/><br/>
-        ProTip: It's actually kind of nice to leave on the background
+        ProTip: It's actually kind of nice to leave on the background<br/><br/>
+        You can back this website <a href="https://www.indiegogo.com/projects/github-audio-music#/" target="_blank">here</a>.
       </div>
       <div class="footer-right-text-block">
         inspired by <a href="http://hatnote.com" target="_blank">hatnote</a><br/>