Add whatsnew entry for simple_efficiency zero load_loss bug

Author: aman-coder03

docs/sphinx/source/whatsnew/v0.13.2.rst

@@ -16,6 +16,10 @@ Deprecations
 
 
 Bug fixes
+* Fixed a division-by-zero error in
+  :py:func:`pvlib.transformer.simple_efficiency` when ``load_loss = 0``.
+  (:issue:`2645`, :pull:`2646`)
+
 ~~~~~~~~~
 
 Enhancements