docs: Remind users to remove --timeout option without socket activation

There is part of our man page that describes how to switch to the
traditional (non-socket) activation but it might still happens sometimes that
there is an extra --timeout option specified for the daemon.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>