update changelog

Author: cailixun

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add Bloch-Redfield master equation solver. ([#473])
 - Implement Bloch Sphere rendering and align style with qutip. ([#472], [#480], [#485], [#487], [#489])
 - Add `Base.copy` method for `AbstractQuantumObject`. ([#486])
+- Add documentation for Bloch-Redfield master equation. ([#493])
 
 ## [v0.31.1]
 Release date: 2025-05-16
@@ -241,3 +242,4 @@ Release date: 2024-11-13
 [#486]: https://github.com/qutip/QuantumToolbox.jl/issues/486
 [#487]: https://github.com/qutip/QuantumToolbox.jl/issues/487
 [#489]: https://github.com/qutip/QuantumToolbox.jl/issues/489
+[#493]: https://github.com/qutip/QuantumToolbox.jl/issues/493