[doc] Update release notes (#4198)

docs/pages/release_notes.md

@@ -20,6 +20,7 @@ This is a {{ site.pmd.release_type }} release.
 
 ### External Contributions
 * [#4184](https://github.com/pmd/pmd/pull/4184): \[java]\[doc] TestClassWithoutTestCases - fix small typo in description - [Valery Yatsynovich](https://github.com/valfirst) (@valfirst)
+* [#4198](https://github.com/pmd/pmd/pull/4198): \[doc] Add supported CPD languages - [Jeroen van Wilgenburg](https://github.com/jvwilge) (@jvwilge)
 
 {% endtocmaker %}