Add description of CFEngine and links to learn more (#320)

* Add description of CFEngine and links to learn more

* Update CFEngine section to add content and fix formatting

Put each paragraph sentence on its own line, per the style guide.

config_management.rst

@@ -243,8 +243,19 @@ Below is an example of a manifest that uses this pattern to install and configur
 The package resource makes sure the software and its config file are installed, the config file depends on the package package resource, and 
 the service subscribes to the changes in the config file.
 
-Cfengine 3
+CFEngine 3
 ==========
+"In 2008, after more than five years of research, CFEngine 3 was introduced, which incorporated promise theory as 'a way to make CFEngine both simpler and more powerful at the same time', according to Burgess."
+`https://en.wikipedia.org/wiki/CFEngine <https://en.wikipedia.org/wiki/CFEngine>`_
+
+"If you are looking for a fast and highly scalable configuration management tool for your IT infrastructure, you should give CFEngine a try. 
+Though the functionality it offers is quite similar to that offered by other popular tools such as Puppet and Chef, CFEngine has a much smaller footprint, both in terms of memory and CPU utilization, and is generally faster because it is written in C and thus runs natively on the OS.",  
+`CFEngine tutorial on DigitalOcean.com <https://www.digitalocean.com/community/tutorials/how-to-install-and-use-cfengine-community-edition-on-ubuntu-14-04>`_
+
+To learn more see:
+`CFEngine Primer <https://digitalelf.net/cf-primer/>`_,
+`CFEngine Tutorial <http://www.cfenginetutorial.org/>`_,
+`CFEngine Learning Center <https://cfengine.com/learn/>`_,
 
 SaltStack
 =========