The page about PHP in the docs doesn’t explain how to use Xdebug. I had
a lof of trouble setting it up the first time, then recently had another
headache trying to get it to work again, because the value for `adapter`
had changed from `PHP` to `Xdebug`.

It’s likely that my example config isn’t perfect or has redundant stuff
or whatever, feel free to amend it.

I also took the liberty to set the Phpactor and Intelephense headings to
level 3 because I felt like they were part of "Choosing a language
server."

Release Notes:

- N/A