Add linked list document in Korean

[trustyoo86]

Add translated Linked List in Korean.

[codecov]

Codecov Report

Merging #448 into master will not change coverage.
The diff coverage is n/a.

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##           master   #448   +/-   ##
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  Coverage     100%   100%           
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  Files         149    149           
  Lines        2612   2612           
  Branches      434    434           
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  Hits         2612   2612

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[trekhleb]

The linked-list/README.ko-KR.md file already exists in the repo. I'm closing this diff for now, but feel free to adjust the existing Korean translation if needed.