backlink added

Author: collaboratewithakash

core-kotlin-modules/core-kotlin-9/README.md

@@ -3,3 +3,4 @@
 - [Find Least Common Multiple of Two Numbers in Kotlin](https://www.baeldung.com/kotlin/lcm)
 - [Calculate Greatest Common Divisor in Kotlin](https://www.baeldung.com/kotlin/gcd)
 - [Kotlin ?.let() vs if not null](https://www.baeldung.com/kotlin/let-vs-if-not-null)
+- [Util Classes in Kotlin](https://www.baeldung.com/kotlin/utility-class)