code: func (g *GPG) Sign(ctx context.Context, in string, sigf string) error {
  	signKeys := g.SigningKeys()
  	if len(signKeys) < 1 {
  		return fmt.Errorf("no signing keys available")
  	}
  
  	sigfh, err := os.OpenFile(sigf, os.O_WRONLY|os.O_CREATE, 0644)
  	if err != nil {
  		return err
  	}
  	defer sigfh.Close()
  
  	wc, err := clearsign.Encode(sigfh, signKeys[0].PrivateKey, nil)
  	if err != nil {
  		return err
  	}
  	infh, err := os.Open(in)
  	if err != nil {
  		return err
  	}
  	defer infh.Close()
  
  	if _, err := io.Copy(wc, infh); err != nil {
  		return err
  	}
  	return wc.Close()
  }
docs: // Sign is not implemented