code: func ShowAppHelp(c *Context) (err error) {
  	if c.App.CustomAppHelpTemplate == "" {
  		HelpPrinter(c.App.Writer, AppHelpTemplate, c.App)
  		return
  	}
  	customAppData := func() map[string]interface{} {
  		if c.App.ExtraInfo == nil {
  			return nil
  		}
  		return map[string]interface{}{
  			"ExtraInfo": c.App.ExtraInfo,
  		}
  	}
  	HelpPrinterCustom(c.App.Writer, c.App.CustomAppHelpTemplate, c.App, customAppData())
  	return nil
  }
docs: // ShowAppHelp is an action that displays the help.