Adopt Contributor Covenant
Adopt Contributor Covenant

Summary:
In order to foster healthy open source communities, we're adopting the
[Contributor Covenant](https://www.contributor-covenant.org/). It has been
built by open source community members and represents a shared understanding of
what is expected from a healthy community.

Reviewed By: josephsavona, danobi, rdzhabarov

Differential Revision: D17104640

fbshipit-source-id: d210000de686c5f0d97d602b50472d5869bc6a49

facebook/SoLoader,facebook/SoLoader,facebook/SoLoader