message: add decorator example
diff: @@ -400,6 +400,24 @@ const View = () => <>
  <div>black</div>
  </>
  app.render(document.body, <View />);
  +`
  + },
  + {
  + name: '@on Decorator',
  + code: `// @on Decorator
  +class Counter extends Component {
  + state = 0;
  +
  + @on()
  + add = (state, delta) => state + delta;
  +
  + view = state => <>
  + <h1>{state}</h1>
  + <button $onclick={['add', -1]}>-1</button>
  + <button $onclick={['add', +1]}>+1</button>
  + </>;
  +}
  +app.render(document.body, <Counter />);
  `
  }
  ];
  