DOC: Update whatsnew in v0.20.0 to include origin parameter

Author: sumitbinnani

doc/source/whatsnew/v0.20.0.txt

@@ -20,7 +20,7 @@ Check the :ref:`API Changes <whatsnew_0200.api_breaking>` and :ref:`deprecations
 
 New features
 ~~~~~~~~~~~~
-
+- ``pd.to_datetime`` has a new parameter, ``origin``, to define an offset for ``DatetimeIndex`` (:issue:`11276`, :issue:`11745`)