docs: Add Korean translation link

Created by: alexkoala

repo: twbs-kr/getbootstrap.kr site: getbootstrap.kr

site/data/translations.yml

@@ -17,3 +17,8 @@
   code: ja
   description: Bootstrap 4 日本語リファレンス
   url: https://getbootstrap.jp/
+
+- name: Korean
+  code: ko
+  description: Bootstrap 4 한국어 문서
+  url: https://getbootstrap.kr/