Docker overview - add app packaging & OS config automation analogies

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Docker overviews sometimes focus on the top-down description with analogies to Docker being a lightweight VM or similar. A bottom-up context is, instead, an analogy with application dependency packaging & installers. For example, walking through: create a component->add dependent components to create a package->add external library dependencies->add OS config dependencies, e.g., FS directories, other apps->package all of these into an installer (sometimes with OS config automation, e.g., puppet/chef/ansible/salt). You can then think of a container as an alternative to an installer/OS config automation. It packages all dependencies together including some OS config dependencies -- the container is like a post-install/post-config packaging of the application.