Update README.md

Author: amitshekhariitbhu

README.md

@@ -969,6 +969,7 @@ public class User {
 - [Infix notation in Kotlin](https://outcomeschool.com/blog/infix-notation-in-kotlin) - Infix notation in Kotlin
 - [Open keyword in Kotlin](https://outcomeschool.com/blog/open-keyword-in-kotlin) - Open keyword in Kotlin
 - [Companion object in Kotlin](https://outcomeschool.com/blog/companion-object-in-kotlin) - Companion object in Kotlin
+- [Extension function in Kotlin](https://outcomeschool.com/blog/extension-function-in-kotlin) - Extension function in Kotlin
 - [How does the Kotlin Multiplatform work?](https://outcomeschool.com/blog/how-does-the-kotlin-multiplatform-work) - How does the Kotlin Multiplatform work?
 
 ## Join **Outcome School** and get high paying tech job: [Outcome School](https://outcomeschool.com)