Add README_KR.md

[HyeongminLEE]

I finally translated the readme file into Korean.
Please review and merge it.

Thanks!

[codecov]

Codecov Report

Merging #620 (c49e974) into master (cc22f2f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #620   +/-   ##
=======================================
  Coverage   89.32%   89.32%           
=======================================
  Files          54       54           
  Lines        3925     3925           
=======================================
  Hits         3506     3506           
  Misses        419      419           

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[haiyangdeperci]

Superseded by #621