Update demo copyright headers.

demo/tailwind.config.js

@@ -1,3 +1,9 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+// All rights reserved.
+
+// This source code is licensed under the license found in the
+// LICENSE file in the root directory of this source tree.
+
 /** @type {import('tailwindcss').Config} */
 module.exports = {
   content: ["./src/**/*.{html,js,tsx}"],