Update CHANGELOG

Author: PowerKiKi

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 - Add Cell Address Helper to provide conversions between the R1C1 and A1 address formats [#1558](https://github.com/PHPOffice/PhpSpreadsheet/pull/1558)
 - Add ability to edit Html/Pdf before saving [#1499](https://github.com/PHPOffice/PhpSpreadsheet/pull/1499)
 - Add ability to set codepage explicitly for BIFF5 [#1018](https://github.com/PHPOffice/PhpSpreadsheet/issues/1018)
-- Added support for the WEBSERVICE function
+- Added support for the WEBSERVICE function [#1409](https://github.com/PHPOffice/PhpSpreadsheet/pull/1409)
 
 ### Fixed