Add example for regex_replace using named groups

docsite/rst/playbooks_filters.rst

@@ -520,6 +520,9 @@ To replace text in a string with regex, use the "regex_replace" filter::
     # convert "foobar" to "bar"
     {{ 'foobar' | regex_replace('^f.*o(.*)$', '\\1') }}
 
+    # convert "localhost:80" to "localhost, 80" using named groups
+    {{ 'localhost:80' | regex_replace('^(?P<host>.+):(?P<port>\\d+)$', '\\g<host>, \\g<port>') }}
+
 .. note:: Prior to ansible 2.0, if "regex_replace" filter was used with variables inside YAML arguments (as opposed to simpler 'key=value' arguments),
    then you needed to escape backreferences (e.g. ``\\1``) with 4 backslashes (``\\\\``) instead of 2 (``\\``).