Add code of conduct

code_of_conduct.md

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+# Contributor Code of Conduct
+
+As contributors and maintainers of this project, we pledge to respect
+all people who contribute through reporting issues, posting feature
+requests, updating documentation, submitting pull requests or patches,
+and other activities.
+
+We are committed to making participation in this project a
+harassment-free experience for everyone, regardless of level of
+experience, gender, gender identity and expression, sexual
+orientation, disability, personal appearance, body size, race, age, or
+religion.
+
+Examples of unacceptable behavior by participants include the use of
+sexual language or imagery, derogatory comments or personal attacks,
+trolling, public or private harassment, insults, or other
+unprofessional conduct.
+
+Project maintainers have the right and responsibility to remove, edit,
+or reject comments, commits, code, wiki edits, issues, and other
+contributions that are not aligned to this Code of Conduct. Project
+maintainers who do not follow the Code of Conduct may be removed from
+the project team.
+
+Instances of abusive, harassing, or otherwise unacceptable behavior
+may be reported by opening an issue or contacting one or more of the
+project maintainers.
+
+This Code of Conduct is adapted from the
+[Contributor Covenant](http:contributor-covenant.org), version 1.0.0,
+available at
+[http://contributor-covenant.org/version/1/0/0/](http://contributor-covenant.org/version/1/0/0/)