docs(centaur): 更新CONTRIBUTING文档

CONTRIBUTING.md

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+# Contributing to Centaur
+
+:+1::tada: First off, thanks for taking the time to contribute! :tada::+1:
+
+This project adheres to the Contributor Covenant [code of conduct](CODE_OF_CONDUCT.md).
+By participating, you are expected to uphold this code. Please report unacceptable
+behavior to kaiyu.shan@outlook.com.
+
+The following is a set of guidelines for contributing to Centaur.
+These are just guidelines, not rules, use your best judgment and feel free to
+propose changes to this document in a pull request.