Add to whatsnew.rst

Author: junukitashepard

doc/whatsnew.rst

@@ -32,6 +32,7 @@ Next release
 - Update documentation for
   :doc:`project/efc` (:pull:`426`) and
   :doc:`project/elevate` (:pull:`427`).
+- New module :mod:`.tools.bilateralize` for bilateralizing scenarios (:pull:`438`).
 
 v2025.9.9
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