CONFIG: Add session_recording section
    
    Add information on "session_recording" config section, having three
    options: "scope", "users", and "groups".
    
    The section is intended for disabling session recording ("scope = none",
    default), enabling session recording for all users ("scope = all"), and
    enabling it for some specific users and/or groups ("scope = some",
    "users = <users>", "groups = <groups>").
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>