Update CHANGELOG.md

Author: oleibman

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Added
 
-- Nothing yet.
+- Method for duplicating worksheet in spreadsheet. [PR #4315](https://github.com/PHPOffice/PhpSpreadsheet/pull/4315)
 
 ### Changed