docs: add Chinese README translation (README_CN.md)

[TravelZero]

概述

新增简体中文 README 翻译（README_CN.md），方便中文社区开发者快速上手 SimpleFOC。

SimpleFOC 在国内嵌入式圈子关注度持续上升，但官方文档只有英文。这篇翻译降低了中文开发者的入门门槛。

改动内容

• 新增 README_CN.md：中文版 README，完整覆盖英文版核心内容
• 修改 README.md：底部添加中文文档链接

翻译覆盖

• 项目介绍与功能一览
• 支持的硬件平台列表
• 5 分钟快速上手教程（含可运行示例代码）
• Arduino IDE / PlatformIO 安装指南
• 文档与资源链接
• 贡献指南
• 常见问题解答

译者

困困困困好困啊

Type of change

• Documentation update

[runger1101001]

Thank you for providing this. Unfortunately I don’t speak any Chinese, so I can’t check anything about this PR 😅

[TravelZero]

Thanks for the response! Totally understand the language barrier.

Here's what this PR does in English:

• Adds README_CN.md — a Chinese translation that mirrors the structure of the English README
• Covers: project intro, features, supported hardware, quick-start guide (with same code examples), installation, docs links, contribution guide, FAQ
• Adds a one-line link at the bottom of README.md pointing to the Chinese version

No code changes, no logic changes — pure documentation. The content is a translation of what already exists in English.

If you prefer, I'm happy to:

1. Add a disclaimer at the top: "⚠️ 这是社区翻译，以 英文版 为准" (This is a community translation, the English version is authoritative)
2. Wait for a Chinese-speaking reviewer if you know one
3. Any other suggestions

Thanks for maintaining SimpleFOC! 🙌

[jaguilar]

How could the README be kept up to date given none of the maintainers speak Chinese? I have never seen an open source project with a README in anything other than English.