Add sdflib changelog item.

PiperOrigin-RevId: 781106659
Change-Id: If4f151468f65095916d76cea2627779640bd5d29

Author: quagla

doc/changelog.rst

@@ -4,8 +4,13 @@ Changelog
 
 Upcoming version (not yet released)
 -----------------------------------
+
+General
+^^^^^^^
 - Added the :ref:`insidesite<sensor-insidesite>` sensor, for checking if an object is inside the volume of a site.
   It is useful for triggering events in surrounding environment logic.
+- Removed the SdfLib plugin and the dependency on `SdfLib` <https://github.com/UPC-ViRVIG/SdfLib>`__. SDFs are now
+  supported natively in mjModel.
 
 Version 3.3.4 (July 8, 2025)
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