Add readme
Summary: Ref T1526
Test Plan: Przejrzeć readme
Reviewers: #reviewers, arkadiusz-wieczorek, kuba-orlik
Reviewed By: #reviewers, arkadiusz-wieczorek, kuba-orlik
Subscribers: kuba-orlik, arkadiusz-wieczorek
Maniphest Tasks: T1526
Differential Revision: https://hub.sealcode.org/D623