Summary:
Facebook Open Source provides a Code of Conduct statement for all projects to follow, to promote a welcoming and safe open source community.
Exposing the COC via a separate markdown file is a standard being promoted by Github via the Community Profile in order to meet their Open Source Guide's recommended community standards.
Adding this file will improve the [Infer community profile](https://github.com/facebook/infer/community) checklist and increase the visibility of our COC.
Reviewed By: jvillard
Differential Revision: D6724173
fbshipit-source-id: 88e6f37
Mehdi Bouaziz