Graphite: Add link to main development site and issue tracker

Change-Id: I8f7777c1234a69e1851b8f4f4e8afc8466cc2e06
Reviewed-on: https://gerrit.libreoffice.org/13918Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

external/graphite/README

@@ -2,3 +2,6 @@ Library for providing rendering capabilities for complex non-Roman writing syste
 
 From:
 [http://graphite.sil.org/]
+
+Development:
+[http://projects.palaso.org/projects/graphitedev]