title: mqtt serial message without ethernet
body: <p>everywhere I look, if it comes to MQTT messaging, it is all over Ethernet.  Unfortunately, I do not have Ethernet wires available.</p>
  
  <p>I am automating my home, wanting to use mqtt as messaging service.  My buttons give a signal (like light 'on') to an arduino board running a mqtt client.  How do i put out the mqtt message on the serial lines so the transmitted message can be straight forwardly be picked up by an mqtt broker, without using the ethernet cables?</p>