code: def add_subtask(self, task, params={}, **options): 
          
          path = "/tasks/%s/subtasks" % (task)
          return self.client.post(path, params, **options)
docs: Creates a new subtask and adds it to the parent task. Returns the full record
          for the newly created subtask.
  
          Parameters
          ----------
          task : {Id} The task to add a subtask to.
          [data] : {Object} Data for the request