[DOC] Added information about customizing the cookbook with the "wrapper cookbook" pattern

Resources:

* http://dougireton.com/blog/2013/02/16/chef-cookbook-anti-patterns/
* http://realityforge.org/code/2012/11/19/role-cookbooks-and-wrapper-cookbooks.html
* http://stackoverflow.com/questions/15933157/replacing-a-template-in-a-wrapper-cookbook/15935161#15935161

Related: #152