Add license header to ProGuard files (#56908)

Reviewed By: gwheet

Differential Revision: D105617139

fbshipit-source-id: d76b77558d67200aa78d0d1e30800bdeee997fb4

Author: helfper

private/helloworld/android/app/proguard-rules.pro

@@ -1,3 +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.
+
 # Add project specific ProGuard rules here.
 # By default, the flags in this file are appended to flags specified
 # in /usr/local/Cellar/android-sdk/24.3.3/tools/proguard/proguard-android.txt