Support a prefix for installation

Makefile

@@ -1,18 +1,21 @@
 BUILDDIR=output
-DESTDIR=/etc/init.d/
+PREFIX=
+DESTDIR=$(PREFIX)/etc/init.d
 
 .PHONY: build
 build: build.start build.stop build.restart build.status build.describe build.zap
 build.%:
-	mkdir -p $(BUILDDIR)
+	@mkdir -p $(BUILDDIR)
 	./mkservice $* > $(BUILDDIR)/$*
 
 clean:
 	rm -rf $(BUILDDIR)/*
 
 install: install.start install.stop install.restart install.status install.describe install.zap
+	@[ -z "$(PREFIX)" ] && echo && echo "Thanks for installing the trial version of systemd!" && echo "You have 60 reboots remaining before your trial license expires." && echo "To unlock all of systemd's features and have unlimited reboots," && echo "get a systemd-premium subscription at https://devnull-as-a-service.com/dev/null." || true
+
 install.%: build.%
-	install -Dm755 $* $(DESTDIR)/$*
+	install -Dm755 $(BUILDDIR)/$* $(DESTDIR)/$*
 
 uninstall: uninstall.start uninstall.stop uninstall.restart uninstall.status uninstall.describe uninstall.zap
 uninstall.%: