Provide separate section for "Projects which use mingw-cross-env"

doc/index.html

@@ -127,6 +127,7 @@
     </ul>
     <ul>
         <li><a href="#see-also"         >See also</a></li>
+        <li><a href="#used-by"          >Used by</a></li>
     </ul>
 </div>
 
@@ -1914,8 +1915,10 @@ https://...</pre>
         <a href="http://www.wxwidgets.org/">wxWidgets project</a>
     </li>
     </ul>
+</div>
 
-    <h3 id="used-by">Projects which use mingw-cross-env</h3>
+<div class="section">
+<h2 id="used-by">Projects which use mingw-cross-env</h2>
 
     <ul class="compact-list">
     <li>