title: Trying to detect new joiners of a Facebook group, so I can send them a welcome message via the API
body: <p>Is there a way of sending a automated welcome message to a user
  after he/she joins a facebook group?</p>
  
  <p>I have tried searching facebook developers graph api but was out of luck. If any one has any idea please share</p>
  
  <p>Thanks</p>