Add an early example of a mutable type inspired by namedtuple.

pep-0557.rst

@@ -99,6 +99,9 @@ Some examples include:
 
 - The popular attrs [#]_ project.
 
+- George Sakkis' recordType recipe [#]_, a mutable data type inspired
+  by collections.namedtuple.
+
 - Many example online recipes [#]_, packages [#]_, and questions [#]_.
   David Beazley used a form of data classes as the motivating example
   in a PyCon 2013 metaclass talk [#]_.
@@ -899,6 +902,9 @@ References
 .. [#] attrs project on github
        (https://github.com/python-attrs/attrs)
 
+.. [#] George Sakkis' recordType recipe
+       (http://code.activestate.com/recipes/576555-records/)
+
 .. [#] DictDotLookup recipe
        (http://code.activestate.com/recipes/576586-dot-style-nested-lookups-over-dictionary-based-dat/)