Add code of conduct
Add code of conduct

Summary: Adds our code of conduct

Reviewed By: sjkirby

Differential Revision: D10452256

fbshipit-source-id: 4aa516794cfb4ab4ad8990d8c5e130a19804ee51

facebook/screenshot-tests-for-android,facebook/screenshot-tests-for-android,facebook/screenshot-tests-for-android,facebook/screenshot-tests-for-android