Add Code of Conduct

Summary: Adding a code of conduct in-line with all of FB's OSS.

Reviewed By: marekcirkos

Differential Revision: D12838651

fbshipit-source-id: 35cc497bc99c81306a08db6480378a0cc84d3617

CODE_OF_CONDUCT.md

@@ -0,0 +1,5 @@
+# Code of Conduct
+
+Facebook has adopted a Code of Conduct that we expect project participants to adhere to.
+Please read the [full text](https://code.fb.com/codeofconduct/)
+so that you can understand what actions will and will not be tolerated.