Add Trix to list of examples; closes jashkenas#4227

Author: GeoffreyBooth

documentation/index.html

@@ -1233,7 +1233,7 @@ <h2>
 
     <ul>
       <li>
-        <b>github</b>’s <a href="http://hubot.github.com/">Hubot</a>,
+        <b>GitHub</b>’s <a href="http://hubot.github.com/">Hubot</a>,
         a friendly IRC robot that can perform any number of useful and useless tasks.
       </li>
       <li>
@@ -1253,9 +1253,12 @@ <h2>
         the Bolo tank game for modern browsers.
       </li>
       <li>
-        <b>github</b>’s <a href="https://atom.io/">Atom</a>,
+        <b>GitHub</b>’s <a href="https://atom.io/">Atom</a>,
         a hackable text editor built on web technologies.
       </li>
+      <li>
+        <b>Basecamp</b>’s <a href="https://trix-editor.org/">Trix</a>, a rich text editor for web apps.
+      </li>
     </ul>
 
     <h2>