Update README.md

Author: rcalago

core-kotlin-modules/core-kotlin-10/README.md

@@ -8,4 +8,5 @@
 - [Calling Private Methods of a Class From Outside the Class](https://www.baeldung.com/kotlin/private-methods-outside-class)
 - [Pass a Function as Parameter to Another in Kotlin](https://www.baeldung.com/kotlin/function-parameter-high-order)
 - [Accessing Methods Outside Companion Object in Kotlin](https://www.baeldung.com/kotlin/companion-object-external-methods)
+- [Accessing Private Java Fields via Kotlin Extension Functions](https://www.baeldung.com/kotlin/extension-functions-private-fields)