Update v0.13.1.rst

Author: RDaxini

docs/sphinx/source/whatsnew/v0.13.1.rst

@@ -29,6 +29,9 @@ Documentation
 ~~~~~~~~~~~~~
 * Substantiate definitions of solar/surface azimuth/zenith and aoi on the
   :ref:`nomenclature` page. (:issue:`2448`, :pull:`2503`)
+* Add a new :ref:`modeling_topics` reference page for the spectrum, documenting 
+  pvlib-python's spectrum functionality, which icnludes a comparison table of spectral
+  mismatch estimation models. (:issue:`2329`, :pull:`2353`)
 
 
 Testing