add netscaler content

[ngksternhagen]

Please consider this pull request with content about Citrix Netscaler.

This content is based on the fine book Troubleshooting Netscaler by Raghu Varma Tirumalaraju. I did not copy any content directly, but we might still consider crediting the original source or providing a link. I didn't see citations elsewhere in the repo, so I was not sure how to handle this.

My totally unqualified opinion is that it's OK (not risky to the opsschool project, and not harmful to Mr. Tirumalaraju) to include the content as is. But I think it would be good to provide a link out of courtesy.

Troubleshooting Netscaler
ISBN-10: 1782175350
ISBN-13: 978-1782175353

[miketheman]

Thanks for your contribution!
How identical is the content to the source?

As for citations, I think we have a few, and they follow this model: http://www.sphinx-doc.org/en/stable/rest.html#citations
An example is here: http://www.opsschool.org/en/latest/shells_101.html#introduction-to-bash