docs: update quickstart information (#1128)

Author: Arantiryo

website/docs/index.mdx

@@ -67,11 +67,16 @@ Install this library with peer dependencies:
 Then, import and use individual components:
 
 ```jsx
-import { Doughnut } from 'react-chartjs-2';
+import { Chart as ChartJS, ArcElement, Tooltip, Legend } from "chart.js";
+import { Doughnut } from "react-chartjs-2";
+
+ChartJS.register(ArcElement, Tooltip, Legend);
 
 <Doughnut data={...} />
 ```
 
+To learn more about importing and registering elements see [tree-shaking](https://react-chartjs-2.js.org/docs/migration-to-v4/#tree-shaking).
+
 :::tip Need an API to fetch data?
 Please consider [Cube](https://cube.dev/?ref=eco-react-chartjs), an open-source API for data apps.
 :::