Update free-courses-ko.md (#6379)

* Update free-courses-ko.md

* Update free-courses-ko.md

courses/free-courses-ko.md

@@ -19,6 +19,7 @@
   * [AngularJS](#angularjs)
   * [Node.js](#node.js)
   * [React.js](#react.js)
+* [Kotlin](#kotlin)
 * [Linux](#linux)
 * [Machine Learning](#machine-learning)
 * [Mathematics](#mathematics)
@@ -164,6 +165,11 @@
 * [React.js 이론부터 실전까지](https://www.youtube.com/playlist?list=PLRx0vPvlEmdCED62ZIWCbI-6G_jcwmuFB)
 
 
+### Kotlin
+
+* [안드로이드 코틀린 기초 강좌](https://www.youtube.com/playlist?list=PLva6rQOdsvQU7QJIg2RHM9wcT11X1S0pj) - 센치한 개발자
+
+
 ### Linux
 
 * [리눅스 및 커널 프로그래밍](http://www.kocw.net/home/search/kemView.do?kemId=1266434) (금오공대 최태영)