code: func NewTimestampCollector() *TimestampCollector {
  	return &TimestampCollector{
  		Description: prometheus.NewDesc(
  			"prometheus_sd_file_mtime_seconds",
  			"Timestamp (mtime) of files read by FileSD. Timestamp is set at read time.",
  			[]string{"filename"},
  			nil,
  		),
  		discoverers: make(map[*Discovery]struct{}),
  	}
  }
docs: // NewTimestampCollector creates a TimestampCollector.