added service and timer files, aswell as Arch PKGBUILD

updated version in main.cpp to be a dependency from cmake

arduino-watchdog-heartbeat.timer

@@ -0,0 +1,8 @@
+[Unit]
+Description=Heartbeat timer for Arduino based watchdog
+
+[Timer]
+OnUnitActiveSec=5min
+
+[Install]
+WantedBy=timers.target