website: add reference to submitting-patches to Contribute tab

In the hope of improving the quality of patches send by newcomers,
add a reference to the submitting-patches section of the manual
to the Contribute tab of the website.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/website/contribute.html

@@ -22,7 +22,8 @@
 	    patchwork</a>.</li>
 	<li>Working on items from the
 	  <a href="http://www.elinux.org/Buildroot#Todo_list">TODO list</a></li>
-	<li>Submitting your own patches through the
+	<li><a href="http://buildroot.org/manual.html#submitting-patches">Submitting
+	  your own patches</a> through the
 	  <a href="http://lists.buildroot.org/mailman/listinfo/buildroot">mailing list
 	</a></li>
       </ul>