linking cbt usage, merge after #1581

Author: cvogt

docs/_includes/toc.html

@@ -12,6 +12,7 @@
             <ul>
                 <li><a href="{{ site.baseurl }}/docs/usage/migrating.html">Migrating from Scala 2</a></li>
                 <li><a href="{{ site.baseurl }}/docs/usage/sbt-projects.html">Using Dotty with sbt</a></li>
+                <li><a href="{{ site.baseurl }}/docs/usage/cbt-projects.html">Using Dotty with cbt</a></li>
             </ul>
         </li>
         <li>