Add Changelog entry

Author: FBumann

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Added
+- Add `facet_row` support to `px.imshow` for creating subplots along an additional dimension [[#5445](https://github.com/plotly/plotly.py/pull/5445)]
+
 ### Fixed
 - Update `numpy.percentile` syntax to stop using deprecated alias [[5483](https://github.com/plotly/plotly.py/pull/5483)], with thanks to @Mr-Neutr0n for the contribution!
   - `numpy` with a version less than 1.22 is no longer supported.