code: func (wp *WorkerPool) PeriodicallyEnqueue(spec string, jobName string) *WorkerPool {
  	schedule, err := cron.Parse(spec)
  	if err != nil {
  		panic(err)
  	}
  
  	wp.periodicJobs = append(wp.periodicJobs, &periodicJob{jobName: jobName, spec: spec, schedule: schedule})
  
  	return wp
  }
docs: // PeriodicallyEnqueue will periodically enqueue jobName according to the cron-based spec.
  // The spec format is based on https://godoc.org/github.com/robfig/cron, which is a relatively standard cron format.
  // Note that the first value is the seconds!
  // If you have multiple worker pools on different machines, they'll all coordinate and only enqueue your job once.