Add a link to the DXR project

DXR is a project developed at Mozilla that implements a code indexing
and browsing utility on top of libclang that has features such as
call graph querying.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@251638 91177308-0d34-0410-b5e6-96231b3b80d8

www/related.html

@@ -82,6 +82,17 @@
         </p>
       </dd>
 
+      <dt>DXR</dt>
+      <dd>
+        <p>
+          <b>Site:</b>
+        <a href="https://github.com/mozilla/dxr#dxr">https://github.com/mozilla/dxr</a>
+        </p>
+        <p>
+        DXR is a code search and navigation tool aimed at making sense of large projects like Firefox. It supports full-text and regex searches as well as structural queries like "Find all the callers of this function."
+        </p>
+      </dd>
+
     </dl>
   </div>
 </body>