Mention filters in changelog

CHANGES.rst

@@ -19,6 +19,15 @@ vmod_re Changes
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+* With the optional ``asfilter`` argument to ``re.regex()``, a varnish
+  filter is created, which can be used to run regular expression
+  substitions on bodies, similar to a flexible mix between
+  ``regsub()`` and ``regsuball()`` on other strings in VCL.
+
+  In this setup,the ``xregex.substitute_match()`` and
+  ``xregex.substitute_all()`` methods can be used to define
+  replacements for matches on the body.
+
 * The ``.match_body()`` method has been added to match a regular
   expression as defined by a ``re.regex()`` object against one of the
   following objects: