Update README.md

Author: rcalago

core-kotlin-modules/core-kotlin-collections-6/README.md

@@ -1,3 +1,4 @@
 ### Relevant Articles: 
 - [Convert a Collection Into an ArrayList in Kotlin](https://www.baeldung.com/kotlin/collection-arraylist-conversion)
 - [Iterate a Collection Referencing Previous Element in Kotlin](https://www.baeldung.com/kotlin/collection-previous-element)
+- [Sorting List with String Dates in Kotlin](https://www.baeldung.com/kotlin/sort-list-string-dates)