Should explain cordis

https://github.com/koishijs/docs/blob/0cd5f59852eb91c34b2130e5de56006f1b4d1ce4/zh-CN/about/faq.md?plain=1#L19

Should explain what `cordis` is or add a link to cordis documents.

> 应当解释 `cordis` 是什么，或者添加一个链接到 cordis 的文档

Open zh-CN/about/faq.md at the section around line 19, where cordis is mentioned. Add a brief explanation of what cordis is or link to its documentation. Done means the FAQ gives readers either that explanation or a direct documentation link.

Written by the indexing model from the issue text.