Add whatsnew entry for #2089

Author: r0hansaxena

docs/sphinx/source/whatsnew/v0.15.1.rst

@@ -38,6 +38,9 @@ Documentation
 * Add AI checkbox to PR template, and auto-generate a comment on PRs
   from first-time contributors regarding AI and contributing guidelines.
   (:issue:`2617`, :pull:`2624`)
+* Fix a broken docstring reference to ``grounddiffuse`` in
+  :py:func:`pvlib.irradiance.poa_components`
+  (:issue:`2089`, :ghuser:`r0hansaxena`)
 
 
 Testing