Add copyright to each file for open sourcing

[jimmytyyang]

Copyright (c) Meta Platforms, Inc. and its affiliates.

This source code is licensed under the MIT license found in the

LICENSE file in the root directory of this source tree.

[jimmytyyang]

#30 Setup instruction -> #43 CI test -> #xx Refactor modules into the third party + update the readme -> #xx add watermark (Facebook XXX), and ask Naoki to help on this -> prepare open-sourcing

[jimmytyyang]

Target open-source date: July 14, 2023 @KavitShah1998

[akshararai]

is this done?