docs with Chinese

[ye4293]

Title: docs with Chinese

Description: (optional)

• add README.cn.md
• add CONTRIBUTING.cn.md
• add CODE_OF_CONDUCT.cn.md
• change CODE_OF_CONDUCT.md
• A directly spliced hyperlink was used because it was not expected to be parsed into bolb/main, but instead was always parsed into tree/. If there is an easy way, you can modify it directly

Motivation: (optional)

• make the project more widely disseminated

Related Issues: (optional)

• #issue-number