code: func FileContainsBytes(fs Fs, filename string, subslice []byte) (bool, error) {
  	f, err := fs.Open(filename)
  	if err != nil {
  		return false, err
  	}
  	defer f.Close()
  
  	return readerContainsAny(f, subslice), nil
  }
docs: // Check if a file contains a specified byte slice.