docs: update docs and CHANGES.rst

CHANGES.rst

@@ -5,6 +5,7 @@ Unreleased
 
 -   Drop support for Python 3.9. :pr:`5730`
 -   Remove previously deprecated code: ``__version__``. :pr:`5648`
+-   Support for using @app.template_filter, @app.template_test, and @app.template_global decorators without parentheses. :pr:`5736`
 
 
 Version 3.1.1

docs/templating.rst

@@ -145,7 +145,11 @@ that.  You can either put them by hand into the
 :attr:`~flask.Flask.jinja_env` of the application or use the
 :meth:`~flask.Flask.template_filter` decorator.
 
-The two following examples work the same and both reverse an object::
+The following examples work the same and all reverse an object::
+
+    @app.template_filter # use the function name as filter name
+    def reverse_filter(s):
+        return s[::-1]
 
     @app.template_filter('reverse')
     def reverse_filter(s):