Added networking section to scenarios.

Section includes:
- twisted
- pyzmq (for zeromq)
- gevent (a mention)

docs/contents.rst.inc

@@ -49,6 +49,7 @@ different scenarios.
    scenarios/cli
    scenarios/gui
    scenarios/db
+   scenarios/network
    scenarios/admin
    scenarios/ci
    scenarios/speed

docs/scenarios/network.rst

@@ -0,0 +1,32 @@
+Networking
+==========
+
+Twisted
+-------
+
+`Twisted <http://twistedmatrix.com/trac/>`_ is an event-driven networking engine. It can be
+used to build applications around many different networking protocols, including http servers
+and clients, applications using SMTP, POP3, IMAP or SSH protocols, instant messaging and 
+`many more <http://twistedmatrix.com/trac/wiki/Documentation>`_.
+
+PyZMQ
+-----
+
+`PyZMQ <http://zeromq.github.com/pyzmq/>`_ is the Python binding for `ZeroMQ <http://www.zeromq.org/>`_,
+which is a high-performance asynchronous messaging library. One great advantage is that ZeroMQ
+can be used for message queuing without message broker. The basic patterns for this are:
+
+- request-reply: connects a set of clients to a set of services. This is a remote procedure call
+  and task distribution pattern.
+- publish-subscribe: connects a set of publishers to a set of subscribers. This is a data 
+  distribution pattern.
+- push-pull (or pipeline): connects nodes in a fan-out / fan-in pattern that can have multiple
+  steps, and loops. This is a parallel task distribution and collection pattern.
+
+For a quick start, read the `ZeroMQ guide <http://zguide.zeromq.org/page:all>`_.
+
+gevent
+------
+`gevent <http://www.gevent.org/>`_ is a coroutine-based Python networking library
+that uses greenlets and libevent event loop.
+