Add documentation key to aoe-discover service file

debian/aoetools.aoe-discover.service

@@ -1,5 +1,6 @@
 [Unit]
 Description=ATA over Ethernet discovery
+Documentation=man:aoe-discover(8)
 BindsTo=sys-devices-virtual-aoe-discover.device
 DefaultDependencies=no
 Conflicts=shutdown.target