xcbuild/CODE_OF_CONDUCT.md

# Code of Conduct

This project adheres to the [Open Code of Conduct](http://todogroup.org/opencodeofconduct/#xcbuild/opensource@fb.com). By participating, you are expected to honor this code.
Add `CODE_OF_CONDUCT.md` what is the change?: Adding a document linking to the Facebook Open Source Code of Conduct, for visibility and to meet Github community standards. why make this change?: It's important that contributors can find the Code of Conduct for a project. xcbuild already links to a Code of Conduct in the Contributing guide, which is great! :) 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. As you can see, adding this file will complete [xcbuild's Community Profile](https://github.com/facebook/xcbuild/community) checklist and increase the visibility of our COC. test plan: Viewing it on my branch - (Flarnie will insert a screenshot) issue: internal task t23481323 2017-12-08 00:19:10 +00:00			`# Code of Conduct`

			`This project adheres to the [Open Code of Conduct](http://todogroup.org/opencodeofconduct/#xcbuild/opensource@fb.com). By participating, you are expected to honor this code.`