Added the documentation for the trusted_hosts option

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3586
Ah, so the purpose of the feature is so that I can "restrict my application to respond to only a sub-set of hosts". Is that accurate? What exactly is the security risk? Or said differently, why would a developer care about this?

I would like to re-word the first few sentences to address the use-case. This is totally invented (since I don't know the real use-case), but for example:

>
If you use the HTTP host for security (e.g., you can only access certain URLs from a specific host), then you should explicitly make sure your application only works for the host names that you're expecting.

That's weak wording... but you get the idea. I'm purposefully being "dumb" (and not looking up more detailson) so that if I understand this feature, then we're good :).

Thanks!