Notify users how it works

switch-branch currently doesn't notify users that it starts updater in the background and the process is not finished when switch-branch finishes (it continues until all packages are updated). It may lead to premature restarts and possibly to break consistency of the system.

It would be good to add a notification, that users should wait and preferably check (in Foris/reForis or by list_notifications) whether everything is done and the system is ready to be restarted.