Add release notes for 0.13.1

Author: dstansby

docs/release.rst

@@ -8,24 +8,22 @@ Release notes
 
 .. _unreleased:
 
-Unreleased
-----------
+0.13.1
+------
 
 Breaking changes
 ~~~~~~~~~~~~~~~~
 * `Zstd.default_level`, `Zstd.min_level`, and `Zstd.max_level` are now class methods
   instead of properties. This means they must now be called like ``Zstd.default_level()``
   instead of ``Zstd.default_level``. This breaking change has been made because Python 3.13
   removes support for class properties.
-  By :user:`David Stansby <dstansby>`
+  By :user:`David Stansby <dstansby>`, :issue:`576`.
 
 Enhancements
 ~~~~~~~~~~~~
-
-
-Fix
-~~~
-
+* Added support for Python 3.13 :user:`David Stansby <dstansby>`, :issue:`576`.
+* Cleaned up the table of contents in the documentation to list codecs by category
+  :user:`David Stansby <dstansby>`, :issue:`458`.
 
 Maintenance
 ~~~~~~~~~~~