Add docs in Korean

[kangthink]

Hi! Thank you for the great project. I hope there would be docs in Korean. I guess README.md and documents in docs would be sufficient. If it is ok, I can work on it. 👍🏻

[trusktr]

Hello! That would definitely be a welcome and awesome contribution! Yeah, I suppose we can follow the existing pattern in the docs folder, f.e. foo.md and foo_ko-KR.md or foo_ko-KP.md (not sure which you are in, but more likely South I guess?).

I think perhaps we should also change to the standard format which seems to be zh_CN and not zh-CN (underscore instead of hyphen.

In that case, perhaps the file convention would be like foo.aa_BB.md. Wdyt?