Update README.md

Author: rcalago

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

@@ -2,3 +2,4 @@
 - [Check if a Collection Is Sorted in Scala](https://www.baeldung.com/scala/check-collection-sorted)
 - [Check if a String Is a Palindrome in Scala](https://www.baeldung.com/scala/string-palindrome-test)
 - [Scala’s Destructuring with the @ Operator](https://www.baeldung.com/scala/destructuring-operator)
+- [Check if Two Strings Are Isomorphic in Scala](https://www.baeldung.com/scala/string-isomorphism)