Update docs with some examples from python ecosystem

Author: gyermolenko

behavioral/command.py

@@ -4,6 +4,9 @@
 """
 *TL;DR80
 Encapsulates all information needed to perform an action or trigger an event.
+
+*Examples in Python ecosystem:
+Django HttpRequest (without `execute` method): https://docs.djangoproject.com/en/2.1/ref/request-response/#httprequest-objects
 """
 
 from __future__ import print_function

behavioral/observer.py

@@ -6,6 +6,10 @@
 
 *TL;DR80
 Maintains a list of dependents and notifies them of any state changes.
+
+*Examples in Python ecosystem:
+Django Signals: https://docs.djangoproject.com/en/2.1/topics/signals/
+Flask Signals: http://flask.pocoo.org/docs/1.0/signals/
 """
 
 from __future__ import print_function

behavioral/template.py

@@ -7,6 +7,9 @@
 *TL;DR80
 Defines the skeleton of a base algorithm, deferring definition of exact 
 steps to subclasses.
+
+*Examples in Python ecosystem:
+Django class based views: https://docs.djangoproject.com/en/2.1/topics/class-based-views/
 """