title: watchOS - Show realtime departure data on complication
body: <p>I have an public transport app with realtime departure data for trains.
  I would like to add a complication that shows the departure time of the next train.</p>
  
  <p>Is it possible to show (or refresh) realtime data on a complication? For example, showing "3 min. to station X." The data could change every minute, based on info that comes from the public transport API.</p>
  
  <p>How should I accomplish this on watchOS 2 or watchOS 3?</p>
  
  <p><em>I know the ETA app shows travel times in a complication, but I'm not sure how they achieve that.</em></p>