Update README.md

Author: johnA1331

core-scala/README.md

@@ -8,3 +8,4 @@ This module contains articles about Scala's core features
 - [Regular Expressions in Scala](https://www.baeldung.com/scala/regular-expressions)
 - [Higher-Order Functions in Scala](https://www.baeldung.com/scala/higher-order-functions)
 - [A Guide to Scala Tuples](https://www.baeldung.com/scala/tuples)
+- [Tail Recursion in Scala](https://www.baeldung.com/scala/tail-recursion)