check for systemd independent of the selected prefix

Makefile

@@ -48,6 +48,13 @@ man:
 		scdoc < "$$f" | gzip > "$$target"; \
 	done
 install:
+	@if [ -e /run/systemd/system ]; then \
+		mkdir -p $(DESTDIR)$(PREFIX)/lib/systemd/system/; \
+		install -Dm644 keyd.service $(DESTDIR)$(PREFIX)/lib/systemd/system/keyd.service; \
+	else \
+		echo "NOTE: systemd not found, you will need to manually add keyd to your system's init process."; \
+	fi
+
 	@if [ "$(VKBD)" = "usb-gadget" ]; then \
 		install -Dm644 src/vkbd/usb-gadget.service $(DESTDIR)$(PREFIX)/lib/systemd/system/keyd-usb-gadget.service; \
 		install -Dm755 src/vkbd/usb-gadget.sh $(DESTDIR)$(PREFIX)/bin/keyd-usb-gadget.sh; \
@@ -60,7 +67,6 @@ install:
 	mkdir -p $(DESTDIR)$(PREFIX)/share/man/man1/
 	mkdir -p $(DESTDIR)$(PREFIX)/share/doc/keyd/
 	mkdir -p $(DESTDIR)$(PREFIX)/share/doc/keyd/examples/
-	mkdir -p $(DESTDIR)$(PREFIX)/lib/systemd/system/
 
 	-groupadd keyd
 	install -m755 bin/* $(DESTDIR)$(PREFIX)/bin/
@@ -69,7 +75,6 @@ install:
 	install -m644 layouts/* $(DESTDIR)$(PREFIX)/share/keyd/layouts
 	install -m644 data/*.1.gz $(DESTDIR)$(PREFIX)/share/man/man1/
 	install -m644 data/keyd.compose $(DESTDIR)$(PREFIX)/share/keyd/
-	install -Dm644 keyd.service $(DESTDIR)$(PREFIX)/lib/systemd/system/
 
 uninstall:
 	rm -rf $(DESTDIR)$(PREFIX)/lib/systemd/system/keyd.service \