added external design pattern documentation links to behavioural patterns.

pypatterns/behavioral/memento.py

@@ -4,6 +4,8 @@ from copy import deepcopy
 class Memento(object):
     """
     Memento class as part of the Memento design pattern.
+
+    External Mediator Pattern documentation: U{https://en.wikipedia.org/wiki/Memento_pattern}
     """
     def __init__(self, state):
         """
@@ -22,6 +24,8 @@ class Memento(object):
 class Originator(object):
     """
     Originator base class as part of the Memento design pattern.
+
+    External Mediator Pattern documentation: U{https://en.wikipedia.org/wiki/Memento_pattern}
     """
     def commit(self):
         """