Add pointer to "React with Hooks" docs port until docs rewrite is ready

Per #3308 , the React team is working on a complete rewrite of the React docs, which is great.

Until then, the tutorials and examples still show classes as the default.

Meanwhile, there's a fantastic port of the current React docs that updates all examples and tutorials to show hooks as the primary approach, at https://reactwithhooks.netlify.app/ .

I'd like to suggest that we add some kind of a header notice or link on the front page and the tutorials that says something like:

We're currently working on a rewrite of the React docs to improve explanations and teach React hooks as the default approach. In the meantime, you may want to look at https://reactwithhooks.netlify.app/ to see these same tutorials written using React hooks.

Commencez par localiser la page d’accueil du site de documentation et les points d’entrée des tutoriels, puis examinez la manière dont les avis ou les liens externes y sont présentés. Le travail est terminé lorsque le lien demandé vers React with Hooks et l’avis explicatif apparaissent sur la page d’accueil et dans les tutoriels, sans attendre la réécriture de la documentation.