Create CODEOFCONDUCT.MD (MystenLabs#987)

Create summary code of conduct in root directory that links into our central code of conduct

CODEOFCONDUCT.MD

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+# Sui Code of Conduct
+
+Sui as an open source project encourages free discussion rooted in respect.
+We endeavor to always be mindful of others' perspectives and ask all
+fellow contributors to do the same. We welcome you to the Sui platform
+and ask you to help us grow it with relevant, on-point contributions.
+
+## Our pledge
+
+We as members, contributors, and leaders pledge to make participation in our
+community a harassment-free experience for everyone, regardless of age, body
+size, visible or invisible disability, ethnicity, sex characteristics, gender
+identity and expression, level of experience, education, socio-economic status,
+nationality, personal appearance, race, caste, color, religion, or sexual
+identity and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming,
+diverse, inclusive, and healthy community.
+
+## More information
+
+See the central [Sui Code of Conduct](doc/src/contribute/code-of-conduct.md) for
+full details.
+
+Our Code of Conduct is adapted from the [Contributor Covenant][homepage],
+version 2.1, available at
+[https://www.contributor-covenant.org/version/2/1/code_of_conduct.html][v2.1].