[WIP] Cookbook grammar and style fixes

This is a follow-up for #4679 

It Fixes some general issues in grammar, style and readability.

(replaces #4693 which was the wrong target branch)

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | >= 2.3
| Fixed tickets | 
To reply to:

 > @WouterJ Agreed. Do you have a concrete idea?

Hmm, I'm not really sure what we are trying to say in this chapter. But maybe something like "For instance, if external connections come in on the default HTTP port 80" or "Imagine that external connections [...]"

@dbu I think you wrote this, can you please explain a bit more?