I modified README.md (added a Chinese switching button) and added READMEcn.md to translate English into Chinese

[Zhaishis]

trafficstars

I am a Chinese, and I like your project very much. Unfortunately, README.md does not have our Chinese language, so I hope to participate in your language sinicization

Thanks

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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