add changelog entry.

Author: kellertuer

Changelog.md

@@ -6,6 +6,12 @@ The file was started with Version `0.4`.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+* fixes a few typos in the doc strings of matrix update formulae within the quasi-Newton solver.
+
 ## [0.5.27] November 11, 2025
 
 ### Added