Update the React recipe for React v18

[rapaccinim]

The React recipe is not showing a correct example of src/index.js for React v18.

ReactDOM.render is no more used in React v18, instead it's necessary to use ReactDOM.createRoot.

This is a practical working example that can be used:

import ReactDOM from "react-dom/client";
import { App } from "./App";

const root = ReactDOM.createRoot(document.getElementById("app"));
root.render(<App />);