Add systemd service to be installed with debian.

Note: when I remove tha package this file doesn't get removed. Why?
When I update the file and then reinstall portspoof it doesn't get udpated. Why?

debian/portspoof-ng.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=Port Soppfing Service
+After=network.target
+
+[Service]
+ExecStart=/usr/bin/portspoof
+Restart=on-failure
+#StandardOutput=syslog
+
+[Install]
+WantedBy=multi-user.target

debian/portspoof-ng.substvars

@@ -1,3 +0,0 @@
-shlibs:Depends=libc6 (>= 2.18), libgcc1 (>= 1:4.2)
-misc:Depends=
-misc:Pre-Depends=

debian/rules

@@ -26,6 +26,7 @@ binary: binary-arch binary-indep
 	dh_install -a
 	dh_installdocs -a
 	dh_installchangelogs -a
+	dh_systemd_enable -a
 	dh_strip -a
 	dh_compress -a
 	dh_fixperms -a