Create CONTRIBUTING.md

Signed-off-by: Sijie Yang <iyangsj@gmail.com>

CONTRIBUTING.md

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+# Contributing
+
+You are welcome to contribute to TQUIC project. This following documents explains our workflow and work style.
+
+
+## How to contribute codes
+
+- [English version](https://tquic.net/docs/how_to_contribute/contribute_codes)
+
+- [Chinese version](https://tquic.net/zh/docs/how_to_contribute/contribute_codes)
+
+
+## How to contribute documents
+
+- [English version](https://tquic.net/docs/how_to_contribute/contribute_docs)
+
+- [Chinese version](https://tquic.net/zh/docs/how_to_contribute/contribute_docs)