Merge pull request #1511 from tc39/add-coc.md-file

Add CoC.md reference file

CODE_OF_CONDUCT.md

+This repository is a TC39 project and subscribes to its [code of conduct](https://tc39.github.io/code-of-conduct/). It is available at [https://tc39.github.io/code-of-conduct/](https://tc39.github.io/code-of-conduct/). 
+
+To ask a question or report an issue, please email [tc39-conduct-reports@googlegroups.com](mailto:tc39-conduct-reports@googlegroups.com).
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