[real-world uses] Add markdown editor built using CodeMirror

doc/realworld.html

@@ -116,6 +116,7 @@
       <li><a href="https://laborate.io/">Laborate</a> (collaborative coding)</li>
       <li><a href="http://lighttable.com/">Light Table</a> (experimental IDE)</li>
       <li><a href="http://liveweave.com/">Liveweave</a> (HTML/CSS/JS scratchpad)</li>
+      <li><a href="https://github.com/TuvaLabs/markdown-delight-editor">Markdown Delight Editor</a> (extensible markdown editor polymer component)</li>
       <li><a href="http://marklighteditor.com/">Marklight editor</a> (lightweight markup editor)</li>
       <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>