Added code of conduct (mochajs#2832)

Added code of conduct, resolves mochajs#2135 [ci skip]

.github/CODE_OF_CONDUCT.md

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+# Mocha Code of Conduct
+
+## Be friendly and patient
+We understand that everyone has different levels of experience or knowledge in many diverse fields, be it technical or
+non-technical in nature. We also have areas of knowledge we are eager to expand; we want to be a community where people
+can not only contribute, but feel comfortable to ask questions as well and learn along the way. If someone says something
+wrong, or says something accidentally offensive, respond with patience and try to keep it polite and civil. Remember that
+we all were newbies at one point.
+
+## Be welcoming
+We strive to be a community that welcomes and supports people of all backgrounds and identities. This includes, but is not
+limited to, members of any race, ethnicity, culture, national origin, color, immigration status, social and economic class,
+educational level, sex, sexual orientation, gender identity and expression, age, size, family status, political belief,
+religion, and mental and physical ability.
+
+## Be considerate
+Your work will be used by other people, and you in turn will depend on the work of others. Any decision you make will affect
+users and colleagues, and you should take those consequences into account when making decisions. Remember that we’re a world-wide
+community, so you might not be communicating in someone else’s primary language.
+
+## Be respectful
+Not all of us will agree all the time, but disagreement is no excuse for poor behavior and poor manners. We might all
+experience some frustration now and then, but we cannot allow that frustration to turn into a personal attack. It’s important
+to remember that a community where people feel uncomfortable or threatened is not a productive one. Members of the JS Foundation
+community should be respectful when dealing with other members as well as with people outside the JS Foundation community.
+
+## Be careful in the words that you choose
+We are a community of professionals, and we conduct ourselves professionally. Be kind to others. Do not insult or put
+down other participants. Harassment and other exclusionary behavior aren’t acceptable. This includes, but is not limited to:
+
+* Violent threats or language directed against another person.
+* Discriminatory jokes and language.
+* Posting sexually explicit or violent material.
+* Posting (or threatening to post) other people’s personally identifying information (“doxing”).
+* Personal insults, especially those using racist or sexist terms.
+* Unwelcome sexual attention.
+* Advocating for, or encouraging, any of the above behavior.
+* Repeated harassment of others. In general, if someone asks you to stop, then stop.
+
+## When we disagree, try to understand why
+Disagreements, both social and technical, happen all the time and JS Foundation projects are no exception. It is important
+that we resolve disagreements and differing views constructively. Remember that we’re different. The strength of the JS
+Foundation comes from its varied community, people from a wide range of backgrounds. Different people have different
+perspectives on issues. Being unable to understand why someone holds a viewpoint doesn’t mean that they’re wrong. Don’t
+forget that it is human to err and blaming each other doesn’t get us anywhere. Instead, focus on helping to resolve issues
+and learning from mistakes.
+
+Original text courtesy of the Speak Up! project and Django Project.
+
+## QUESTIONS?
+If you have questions, please see the FAQ. If that doesn’t answer your questions, feel free to email conduct@js.foundation.