add tutorial link

Author: James Yu

index.html

@@ -24,7 +24,8 @@ <h1>Parse Todos</h1>
     </div>
 
     <div id="credits">
-      Powered by <a href="https://www.parse.com">Parse</a> using the <a href="https://www.parse.com/docs/js_guide">JavaScript SDK</a>
+      Powered by <a href="https://www.parse.com">Parse</a> using the <a href="https://www.parse.com/docs/js_guide">JavaScript SDK</a>.<br /><br />
+      Learn how we built it in the <a href='https://parse.com/tutorials/todo-app-with-javascript'>tutorial</a>.
     </div>
 
     <!-- Templates -->