Add Korean translation of contributing.md

[min-kim42]

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest master. (If I was asked to make more changes, I have made sure to rebase onto master then too)
• is descriptively named and links to an issue number, i.e. Fixes #123
  Addresses Add Korean Translation #1350

[catarak]

This looks great, thank you ✨