Add realtime.io to real-world uses

Author: marijnh

doc/realworld.html

@@ -67,6 +67,7 @@ <h1><span class="logo-braces">{ }</span> <a href="http://codemirror.net/">CodeMi
       <li><a href="http://qyapp.com">QiYun web app platform</a></li>
       <li><a href="http://ariya.ofilabs.com/2011/09/hybrid-webnative-desktop-codemirror.html">Qt+Webkit integration</a> (building a desktop CodeMirror app)</li>
       <li><a href="http://rascalmicro.com/docs/basic-tutorial-getting-started.html">Rascal</a> (tiny computer)</li>
+      <li><a href="https://www.realtime.io/">RealTime.io</a> (Internet-of-Things infrastructure)</li>
       <li><a href="http://www.sketchpatch.net/labs/livecodelabIntro.html">sketchPatch Livecodelab</a></li>
       <li><a href="http://www.skulpt.org/">Skulpt</a> (in-browser Python environment)</li>
       <li><a href="http://www.solidshops.com/">SolidShops</a> (hosted e-commerce platform)</li>