docs: update Javadoc in Menu annotation (#19318) (#19328)

Co-authored-by: Tomi Virtanen <tltv@vaadin.com>

flow-server/src/main/java/com/vaadin/flow/router/Menu.java

@@ -27,8 +27,9 @@
  * Defines menu information for a route for automatically populated menu.
  * <p>
  * {@link Menu} is used together with {@link Route} to include it automatically
- * in Hilla application's main menu, but only if server routes are being exposed
- * for client-side via 'window.Vaadin.server.views' variable in the client-side.
+ * in Hilla application's main menu, but only if server route is accessible and
+ * {@code frontend/views/@layout.tsx} is used with {@code createMenuItems()}
+ * function to build the menu.
  * </p>
  *
  * @see Route