Merge pull request #761 from Maiklins/KTLN-754-update-readme

Update README.md

Author: Maiklins

core-kotlin-modules/core-kotlin-lang-4/README.md

@@ -7,4 +7,5 @@ This module contains articles about core features in the Kotlin language.
 - [Difference Between !! and ? in Kotlin](https://www.baeldung.com/kotlin/nullability-operators-difference)
 - [Using Kotlin when() Clause for <, <=, >=, and == Comparisons](https://www.baeldung.com/kotlin/when-clause-comparisons)
 - [Difference Between “it” and “this” Keywords in Kotlin](https://www.baeldung.com/kotlin/it-vs-this-keywords)
+- [Data Objects in Kotlin](https://www.baeldung.com/kotlin/data-object-basics)
 - [[<-- prev]](/core-kotlin-modules/core-kotlin-lang-3)