Mention that we are a fork on the about page

Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>

patchwork/templates/patchwork/help/about.html

@@ -6,7 +6,9 @@
 {% block body %}
 
 <p>Patchwork is free software, and is available from the
-<a href="http://jk.ozlabs.org/projects/patchwork/">Patchwork website</a>.</p>
+<a href="https://gitlab.freedesktop.org/patchwork-fdo/patchwork-fdo">Patchwork FDO</a>
+which is forked from the original
+<a href="http://jk.ozlabs.org/projects/patchwork/">Patchwork</a>.</p>
 
 <p>Patchwork is built on the <a href="http://djangoproject.com/">django</a>
 web framework.</p>