Enterprise: show how to configure tools/libraries

[ben]

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As noted in https://github.com/xrd/advanced-github-oreilly/pull/13#issuecomment-102646878:

For example, show how hub works with the enterprise server. Show an example of the ruby library configured to use the API from the enterprise server. And perhaps show how the network topology could be made more secure if services are all hosted inside the firewall.