link to the homepage for support/service (1.1-maint)

otherwise people ONLY reading the docs (and not coming from the
homepage) will miss these options.

docs/support.rst

@@ -1,6 +1,11 @@
+Support
+=======
+
+Support and Services
+--------------------
+
+Please see https://www.borgbackup.org/ for free and paid support and service options.
 
-Security
-========
 
 .. _security-contact: