Update section about use of NetworkManager

https://fedorahosted.org/freeipa/ticket/4156

Reviewed-By: Jan Pazdziora <jpazdziora@redhat.com>
Update resolv.conf nameserver note to reflect real IP address

- Added example of real IP address as the installer inserts a real IP address into resolv.conf.

Reviewed-By: Petr Spacek <pspacek@redhat.com>