add related projects, fix web site url

docs/_themes/local/sidebarusefullinks.html

@@ -3,9 +3,15 @@
 
 <h3>Useful Links</h3>
 <ul>
-  <li><a href="https://borgbackup.github.io/">Main Web Site</a></li>
+  <li><a href="https://borgbackup.github.io/borgbackup/">Main Web Site</a></li>
   <li><a href="https://pypi.python.org/pypi/borgbackup">PyPI packages</a></li>
   <li><a href="https://github.com/borgbackup/borg">GitHub</a></li>
   <li><a href="https://github.com/borgbackup/borg/issues">Issue Tracker</a></li>
   <li><a href="http://librelist.com/browser/borgbackup/">Mailing List</a></li>
 </ul>
+
+<h3>Related Projects</h3>
+<ul>
+  <li><a href="https://borgbackup.github.io/borgweb/">BorgWeb</a></li>
+</ul>
+