🌐 [i18n-KO] Translated Chapter 3 to Korean

[wonhyeongseo]

What does this PR do?

Translated the Chapter 3 of the course to Korean.
Thank you in advance for your review.

Part of #42

Before reviewing

• Check for missing / redundant translations (번역 누락/중복 검사)
• Grammar Check (맞춤법 검사)
• Review or Add new terms to glossary (용어 확인 및 추가)
• Check Inline TOC (e.g. [[lowercased-header]])
• Check live-preview for gotchas (live-preview로 정상작동 확인)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@lewtun May you please review this PR?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.