Move whats-new entry

Author: TomNicholas

doc/whats-new.rst

@@ -38,6 +38,9 @@ Bug fixes
 Documentation
 ~~~~~~~~~~~~~
 
+- Add docstrings for the :py:class:`Index` base class and add some documentation on how to
+  create custom, Xarray-compatible indexes (:pull:`6975`)
+  By `Benoît Bovy <https://github.com/benbovy>`_.
 
 Internal Changes
 ~~~~~~~~~~~~~~~~
@@ -796,9 +799,6 @@ Bug fixes
 Documentation
 ~~~~~~~~~~~~~
 
-- Add docstrings for the :py:class:`Index` base class and add some documentation on how to
-  create custom, Xarray-compatible indexes (:pull:`6975`)
-  By `Benoît Bovy <https://github.com/benbovy>`_.
 - Update merge docstrings. (:issue:`6935`, :pull:`7033`)
   By `Zach Moon <https://github.com/zmoon>`_.
 - Raise a more informative error when trying to open a non-existent zarr store. (:issue:`6484`, :pull:`7060`)