FAQ: Add fail2ban info?

[garrett]

@ecadagiani has a neat bit of information about setting up a config for fail2ban to work with Cockpit.

@ cockpit-project/cockpit#722 (comment)

As this is likely outside the scope of Cockpit (unless we ship an example file), something like this makes sense to document on the website. Perhaps under the FAQ, in an "integration" category. If we had an additional page for tips and tricks, it could exist on that page instead (and we could link that tips & tricks page from the FAQ).