Update README.md

Author: rcalago

scala-core-collections-modules/scala-core-collections-4/README.md

@@ -1,3 +1,4 @@
 ## Relevant Articles
 - [Using filter() and takeWhile() With Collections in Scala](https://www.baeldung.com/scala/filter-takewhile)
 - [Finding Elements in a List using takeWhile() and dropWhile() in Scala](https://www.baeldung.com/scala/list-find-takewhile-dropwhile)
+- [Calculate the Average of a List in Scala](https://www.baeldung.com/scala/list-compute-mean-value)