code: func ReadHash(r io.Reader) (plumbing.Hash, error) {
  	var h plumbing.Hash
  	if err := binary.Read(r, binary.BigEndian, h[:]); err != nil {
  		return plumbing.ZeroHash, err
  	}
  
  	return h, nil
  }
docs: // ReadHash reads a plumbing.Hash from r