Added the documentation for the trusted_hosts option

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | 2.3+
| Fixed tickets | #3586
I would add one more sentence at the end. Something like this:

>
If the incoming request's hostname doesn't match one in this list, the
application won't respond and the user will receive a 500 response:

I wasn't sure initially if maybe if your host wasn't in this list that Symfony still responded but used a different absolute URL (or something like that). This is clear that literally your app won't work at all.