[real-world uses] Add nteract

Author: rgbkrk

doc/realworld.html

@@ -123,6 +123,7 @@ <h2>CodeMirror real-world uses</h2>
       <li><a href="http://www.navigatecms.com">Navigate CMS</a></li>
       <li><a href="https://github.com/soliton4/nodeMirror">nodeMirror</a> (IDE project)</li>
       <li><a href="https://notex.ch">NoTex</a> (rST authoring)</li>
+      <li><a href="https://nteract.io">nteract</a> (interactive literate coding notebook)</li>
       <li><a href="http://oakoutliner.com">Oak</a> (online outliner)</li>
       <li><a href="http://www.greycampus.com/opencampus">OpenCampus</a></li>
       <li><a href="http://clrhome.org/asm/">ORG</a> (z80 assembly IDE)</li>