Update Changelog

Author: oleibman

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Added
 
-- Nothing yet.
+- Add to all readers the option to allow or forbid fetching external images. This is unconditionally allowed now. The default will be set to "allow", so no code changes are necessary. However, we are giving consideration to changing the default. [PR #4543](https://github.com/PHPOffice/PhpSpreadsheet/pull/4543)
 
 ### Removed