code: def add(ctx, short_name, uri, interval, buffer):
      
      wva = get_wva(ctx)
      subscription = wva.get_subscription(short_name)
      subscription.create(uri, buffer, interval)
docs: Add a subscription with a given short_name for a given uri
  
  This command can be used to create subscriptions to receive new pieces
  of vehicle data on the stream channel on a periodic basis.  By default,
  subscriptions are buffered and have a 5 second interval:
  
  \b
      $ wva subscriptions add speed vehicle/data/VehicleSpeed
      $ wva subscriptions show speed
      {'buffer': 'queue', 'interval': 5, 'uri': 'vehicle/data/VehicleSpeed'}
  
  These parameters can be modified by the use of optional arguments:
  
      $ wva subscriptions add rpm vehicle/data/EngineSpeed --interval 1 --buffer discard
      $ wva subscriptions show rpm
      {'buffer': 'discard', 'interval': 1, 'uri': 'vehicle/data/EngineSpeed'}
  
  To view the data coming in as a result of these subscriptions, one can use
  either 'wva subscriptions listen' or 'wva subscriptions graph <name>'.