code: func (s *Action) CompletionZSH(c *cli.Context, a *cli.App) error {
  	comp, err := zshcomp.GetCompletion(a)
  	if err != nil {
  		return err
  	}
  
  	fmt.Fprintln(stdout, comp)
  	return nil
  }
docs: // CompletionZSH returns a zsh completion script