Add systemd service unit to contrib

Apply sed to reflect prefix but don't install it and clean service file in makefile. Add service file to gitignore

.gitignore

@@ -5,5 +5,6 @@ vgcore.*
 config.h
 dunst.1
 org.knopwob.dunst.service
+dunst.systemd.service
 dunstify
 test/test

Makefile

@@ -47,6 +47,7 @@ debug: ${OBJ}
 clean-dunst:
 	rm -f dunst ${OBJ} main.o
 	rm -f org.knopwob.dunst.service
+	rm -f dunst.systemd.service
 
 clean-dunstify:
 	rm -f dunstify
@@ -62,6 +63,7 @@ docs/dunst.1: docs/dunst.pod
 
 service:
 	@sed "s|##PREFIX##|$(PREFIX)|" org.knopwob.dunst.service.in > org.knopwob.dunst.service
+	@sed "s|##PREFIX##|$(PREFIX)|" contrib/dunst.systemd.service.in > dunst.systemd.service
 
 install-dunst: dunst doc
 	mkdir -p ${DESTDIR}${PREFIX}/bin

contrib/dunst.systemd.service.in

@@ -0,0 +1,11 @@
+[Unit]
+Description=Dunst notification daemon
+
+[Service]
+Type=simple
+ExecStart=##PREFIX##/bin/dunst
+Environment=DISPLAY=:0
+
+[Install]
+WantedBy=multi-user.target
+