[real-world uses] Add MVC Playground

doc/realworld.html

@@ -88,6 +88,7 @@
       <li><a href="http://www.mergely.com/">Mergely</a> (interactive diffing)</li>
       <li><a href="http://www.iunbug.com/mihtool">MIHTool</a> (iOS web-app debugging tool)</li>
       <li><a href="http://mongo-mapreduce-webbrowser.opensagres.cloudbees.net/">Mongo MapReduce WebBrowser</a></li>
+      <li><a href="http://mvcplayground.apphb.com/">MVC Playground</a></li>
       <li><a href="https://www.my2ndgeneration.com/">My2ndGeneration</a> (social coding)</li>
       <li><a href="http://www.navigatecms.com">Navigate CMS</a></li>
       <li><a href="https://github.com/soliton4/nodeMirror">nodeMirror</a> (IDE project)</li>