code of conduct (#4)

CODE_OF_CONDUCT.md

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+# Code of conduct
+
+Everyone is invited to participate in Mapbox’s open source projects and public discussions: we want to create a welcoming and friendly environment. Harassment of participants or other unethical and unprofessional behavior will not be tolerated in our spaces. The [Contributor Covenant](http://contributor-covenant.org) applies to all projects under the Mapbox organization and we ask that you please read [the full text](http://contributor-covenant.org/version/1/2/0/).
+
+You can learn more about our open source philosophy on [mapbox.com](https://www.mapbox.com/about/open/).