put prerequisites near top

threejs/lessons/toc.html

@@ -3,6 +3,7 @@
   <ul>
     <li><a href="/threejs/lessons/threejs-fundamentals.html">Fundamentals</a></li>
     <li><a href="/threejs/lessons/threejs-responsive.html">Responsive Design</a></li>
+    <li><a href="/threejs/lessons/threejs-prerequisites.html">Prerequisites</a></li>
     <li><a href="/threejs/lessons/threejs-setup.html">Setup</a></li>
   </ul>
   <li>Solutions</li>
@@ -29,7 +30,6 @@
   </ul>
   <li>Reference</li>
   <ul>
-    <li><a href="/threejs/lessons/threejs-prerequisites.html">Prerequisites</a></li>
     <li><a href="/threejs/lessons/threejs-material-table.html">Material Table</a></li>
   </ul>
 </ul>