znc.service: Improve description, don't fork on your own

The description gets displayed when the service is started and would
output something like "Starting An advanced IRC bouncer". There's
potentially more than one, though, and, thus, the name should at least
be included.

Type=forking should be used as a last resort only. systemd does the
forking itself and, thus, ZNC should be started with the -f switch.

znc.service

@@ -1,11 +1,10 @@
 [Unit]
-Description=An advanced IRC bouncer
+Description=ZNC, an advanced IRC bouncer
 After=network.target
 
 [Service]
-ExecStart=/usr/bin/znc
+ExecStart=/usr/bin/znc -f
 User=znc
-Type=forking
 
 [Install]
 WantedBy=multi-user.target