Add Code of Conduct (#680)

CODE_OF_CONDUCT.md

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+# Code of Conduct
+
+Our community is welcoming to everyone, regardless of their characteristics.
+
+As such, we expect you to treat everyone with respect and contribute to an open and welcoming community.
+
+DO
+- have empathy and be nice to others
+- be respectful of differing opinions, even if you disagree
+- give and accept constructive criticism
+
+DON'T
+- use offensive or derogatory language
+- troll or spam
+- personally attack or harass others
+
+Repetitive violations of these guidelines might get your access to the repository restricted.
+
+
+If you feel like a user is violating these guidelines or feel treated unfairly, please refrain from publicly challenging them and instead contact a Moderator on our Discord server or send an email to vendicated+conduct@riseup.net!