Add changelog entry

Author: saulshanabrook

docs/changelog.md

@@ -4,6 +4,8 @@ _This project uses semantic versioning_
 
 ## UNRELEASED
 
+- Support using facts as union actions, add conversions to multisets, and update multiset examlpe [#382](https://github.com/egraphs-good/egglog-python/pull/382)
+
 ## 12.0.0 (2025-11-16)
 
 - Add support for setting report level with `egraph.set_report_level` [#375](https://github.com/egraphs-good/egglog-python/pull/375)