Update CHANGES for PR #9146

Author: tk0miya

CHANGES

@@ -21,6 +21,7 @@ Features added
 * #8588: autodoc: :confval:`autodoc_type_aliases` now supports dotted name. It
   allows you to define an alias for a class with module name like
   ``foo.bar.BazClass``
+* #3257: autosummary: Support instance attributes for classes
 * #9129: html search: Show search summaries when html_copy_source = False
 * #9120: html theme: Eliminate prompt characters of code-block from copyable
   text