docs: add CHANGELOG entry for overflow-safe cross-unit integer comparisons

Author: mpusz

CHANGELOG.md

@@ -35,6 +35,8 @@ This page documents the version history and changes for the **mp-units** library
 - refactor: representation concepts cleanup
 - refactor: `quantity_spec` call operator constraints improved
 - refactor: `quantity_cast` constraints improved
+- fix: overflow-safe cross-unit integer comparisons using double-width arithmetic
+  (based on original work by [@burnpanck](https://github.com/burnpanck) in #580)
 - fix: dimensionless quantities truncation prevention fixed
 - fix: clang-18 workaround for pragmas not working in a C++ module build
 - fix: `normal_stress` and `shear_stress` fixed to have `stress` as a parent