Suggestion for docs

[sinauq]

What version of Emacs are you running?

29.1

What version of LanguageTool are you running?

remote server

What version of this package are you running?

1.3

What is the current behaviour?

The document is not clear about how to use languagetool's premium server.

What is you expect to happen?

For anyone who might face the same problem, the config should be something like this:

(use-package languagetool
  :config
  (setq
   languagetool-server-url "https://api.languagetoolplus.com"
   languagetool-server-port 443
   languagetool-api-key "XXXX"
   languagetool-username "XXX"
   ))

### What do you do to get this bug?

_No response_