Update free-courses-en.md (#6044)

In this Kotlin course, user will get familiarized with the language syntax, concepts, and libraries, as well as with the basics of OOP.

courses/free-courses-en.md

@@ -556,6 +556,7 @@
 * [Android Kotlin Tutorial: Create Android Apps using Kotlin](https://www.youtube.com/playlist?list=PLlxmoA0rQ-Lw5k_QCqVl3rsoJOnb_00UV) - Sriyank Siddhartha (YouTube)
 * [Developing Android Apps with Kotlin](https://www.udacity.com/course/developing-android-apps-with-kotlin--ud9012) (Udacity)
 * [Kotlin Bootcamp for Programmers](https://www.udacity.com/course/kotlin-bootcamp-for-programmers--ud9011) - Aleks Haecky, Asser Samak, Sean McQuillan (Udacity)
+* [Track: Kotlin Basics](https://hyperskill.org/tracks/18) - Hyperskill, JetBrains (Hyperskill)
 
 
 ### Kubernetes