Update CHANGELOG for PR #5896

Author: ponylang-main

CHANGELOG.md

@@ -25,6 +25,7 @@ All notable changes to the Pony compiler and standard library will be documented
 ### Added
 
 - Add --pass-timings/--pass-timings-json for profiling compiler pass times ([PR #5792](https://github.com/ponylang/ponyc/pull/5792))
+- Add multi-iterator for loop sugar ([PR #5896](https://github.com/ponylang/ponyc/pull/5896))
 
 ### Changed