code: func (f *Form) AddCheckbox(label string, checked bool, changed func(checked bool)) *Form {
  	f.items = append(f.items, NewCheckbox().
  		SetLabel(label).
  		SetChecked(checked).
  		SetChangedFunc(changed))
  	return f
  }
docs: // AddCheckbox adds a checkbox to the form. It has a label, an initial state,
  // and an (optional) callback function which is invoked when the state of the
  // checkbox was changed by the user.