Add changelog

Author: Archmonger

docs/source/about/changelog.rst

@@ -20,6 +20,7 @@ Unreleased
 - :pull:`1251` - Substitute client-side usage of ``react`` with ``preact``.
 - :pull:`1239` - Script elements no longer support behaving like effects. They now strictly behave like plain HTML script elements.
 - :pull:`1255` - The ``reactpy.html`` module has been modified to allow for auto-creation of any HTML nodes. For example, you can create a ``<data-table>`` element by calling ``html.data_table()``.
+- :pull:`1256` - Change ``set_state`` comparison method to check equality with ``==`` more consistently.
 
 **Removed**