Improve API note

Co-authored-by: Tim Hoffmann <[email protected]>

Author: dstansby

doc/api/next_api_changes/removals/30005-DS.rst

@@ -1,7 +1,11 @@
 ``matplotlib.cm.get_cmap``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-If you have the name of a colormap as a `str`, use ``matplotlib.colormaps[name]`` instead.
+Colormaps are now available through the `.Coloarmap.Registry` accessible via
+``matplotlib.colormaps`` or ``plt.colormaps``.
 
-Otherwise `matplotlib.cm.ColormapRegistry.get_cmap` if you have a `str`, `None` or a
-`matplotlib.colors.Colormap` object that you want to convert to a `.Colormap` object.
+If you have the name of a colormap as a sting, you can use direct lookup
+``matplotlib.colormaps[name]``. Alternatively, `matplotlib.colormaps.get_cmap` will
+maintain the existing behavior of additionally passing through `.Colormap` instances
+and converting ``None`` to the default colormap. `plt.get_cmap` will stay as a
+shortcut to `matplotlib.colormaps.get_cmap`.