doc(auth0-blog): add React v18 note

auth0-blog/app/index.jsx

@@ -8,7 +8,7 @@ import Auth0ProviderWithHistory from './auth/auth0-provider-with-history';
 if (process.env.NODE_ENV !== 'production') {
     console.log('development mode');
 }
-//since react 18
+/*ReactDOM.render is no longer supported in React 18. Use createRoot instead.*/
 import { createRoot } from 'react-dom/client';
 //create root container
 const root = createRoot(document.getElementById("root"));