Update CHANGELOG.md

CHANGELOG.md

@@ -5,6 +5,8 @@ Differences Between DuMu<sup>x</sup> 3.3 and DuMu<sup>x</sup> 3.2
 
 - __Dune version__: DuMu<sup>x</sup> now requires Dune >=2.7
 - The DuMu<sup>x</sup> install script has been translated to Python to improve portability. The old shell script will be removed after release 3.3.
+- The velocity reconstruction for immiscible porous-media models has been improved, leading to slightly
+  different velocity fields in the vicinity of Neumann boundaries.
 
 ### Immediate interface changes not allowing/requiring a deprecation period: