Add changelog entry

Author: ValerianRey

CHANGELOG.md

@@ -19,6 +19,7 @@ changes that do not affect the user.
 - Refactored internal verifications in the autojac engine so that they do not run at runtime
   anymore. This should minimally improve the performance and reduce the memory usage of `backward`
   and `mtl_backward`.
+- Improved the implementation of ConFIG to be simpler and safer when normalizing vectors. It should slightly improve the performance of ConFIG and minimally affect its behavior.
 
 ### Fixed