Document behavior of verbatim chunks in key expressions

[jeffective]

Describe the feature

I was trying to query the liveliness of some advanced subscribers.

I was not aware that ** would not match the tokens and instead I needed to query * * /@adv/sub/ * *.

This behavior is not documented in the key expression syntax documentation: https://zenoh.io/docs/manual/abstractions/

Please add this to the documentation.