Separate out FAQ

[Gabirel]

The document could become a huge. One Single FAQ will take a lot of pages.

I think it will better if I can separate them.

[Gabirel]

• [x] Separate out FAQ in en_US

• [x] Separate out FAQ in zh_US

• [x] Update TOC in en_US/README.md

• [x] Update TOC in README.md

• [x] Update TOC in zh_CN/README.md

• [x] Update TOC in README_zh_CN.md