Add missing copyright header (#33106)

This made the build fail since there was no file header comment.

Author: kassens

packages/eslint-plugin-react-hooks/npm/index.d.ts

@@ -1 +1,8 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
 export * from './cjs/eslint-plugin-react-hooks';

packages/eslint-plugin-react-hooks/npm/index.js

@@ -1,3 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
 'use strict';
 
 // TODO: this doesn't make sense for an ESLint rule.