Better NetworkManager instructions

Hi!

Was following the docs to switch the networking to use the NetworkManager tool. This was not enough to replace the default wpa_supplicant stack. The first issue I encountered was that adding the user to the network group as documented was not enough, nmcli still said my user had no permission to connect.

To fix this I had to install and enable the polkitd service. I think this is worth specifying in the documentation!

Also I had another issue with the dns. My /etc/resolv.conf file was not getting overridden by NetworkManager and had to create a manual symlink.

Individua la sezione della documentazione che tratta la configurazione di NetworkManager e confronta le relative istruzioni con la transizione a wpa_supplicant segnalata. Aggiorna le istruzioni in modo da includere l'installazione e l'abilitazione di polkitd e la gestione del collegamento simbolico /etc/resolv.conf; il lavoro è completo quando sia la configurazione dei permessi sia quella del DNS sono spiegate chiaramente.