[Docs/ko] fix typo and grammar, add ko translation

[inyeong-kang]

Problem

• 'Create React App을 설치하는 더 많은 방법은 [공식 문서](https://github.com/facebook/create-react-app#creating-an-app)을 보면된다.' This sentence has typos.
• Comments of codes are not translated into korean.

Solve

• 'Create React App을 설치하는 더 많은 방법은 [공식 문서](https://github.com/facebook/create-react-app#creating-an-app)을 보면된다.'-> Create React App을 설치하는 더 많은 방법은 [공식 문서](https://github.com/facebook/create-react-app#creating-an-app)를 보면 된다.'
• Added korean translation to comments.

[facebook-github-bot]

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