docs(v2): add router implementation note (#2935)

website/docs/docusaurus-core.md

@@ -103,6 +103,12 @@ function Home() {
 }
 ```
 
+:::note
+
+`@docusaurus/router` implements [React Router](https://reacttraining.com/react-router/web/guides/quick-start) and supports its features.
+
+:::
+
 ### `<BrowserOnly/>`
 
 The `<BrowserOnly>` component accepts a `children` prop, a render function which will not be executed during the pre-rendering phase of the build process. This is useful for hiding code that is only meant to run in the browsers (e.g. where the `window`/`document` objects are being accessed). To improve SEO, you can also provide fallback content using the `fallback` prop, which will be prerendered until in the build process and replaced with the client-side only contents when viewed in the browser.