systemd: Provide URL and better description

Let's direct users to the support site when they ask systemd for help
about the service unit, or by looking at error messages.

Also, let's adjust the description to be more pleasing to the eyes. The
previous long description with uncommon formatting really stuck out in
the boot logs.

Signed-off-by: Kai Krakow <kai@kaishome.de>

scripts/beesd@.service.in

@@ -1,5 +1,6 @@
 [Unit]
-Description=Bees - Best-Effort Extent-Same, a btrfs deduplicator daemon: %i
+Description=Bees (%i)
+Documentation=https://github.com/Zygo/bees
 After=sysinit.target
 
 [Service]