Add changelog

Author: albertomercurio

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)
 
 - Improve Bloch sphere rendering for animation. ([#520])
+- Add `sortby` and `rev` keyword arguments to eigensolvers. ([#546])
 
 ## [v0.34.0]
 Release date: 2025-07-29
@@ -295,3 +296,4 @@ Release date: 2024-11-13
 [#515]: https://github.com/qutip/QuantumToolbox.jl/issues/515
 [#517]: https://github.com/qutip/QuantumToolbox.jl/issues/517
 [#520]: https://github.com/qutip/QuantumToolbox.jl/issues/520
+[#546]: https://github.com/qutip/QuantumToolbox.jl/issues/546