code: func (is *store) GetLastUpdated(id ID) (time.Time, error) {
  	bytes, err := is.fs.GetMetadata(id.Digest(), "lastUpdated")
  	if err != nil || len(bytes) == 0 {
  		// No lastUpdated time
  		return time.Time{}, nil
  	}
  	return time.Parse(time.RFC3339Nano, string(bytes))
  }
docs: // GetLastUpdated time for the image ID