Announce /etc/rc.d/sendmail does not work in default should be made at use time.

Hi, all

I found /etc/rc.d/sendmail does not work in default. To make
use of sendmail, I had to be done with
`cp /usr/share/examples/sendmail/mailer.conf /etc/mail'.

I saw why default MTA changed to dma:

	commit a67b925ff3e58b072a60b633e442ee1d33e47f7f
	Author: Baptiste Daroussin <bapt@FreeBSD.org>
	Date:   Thu Oct 13 11:37:21 2022 +0200
	
	    mail: make The Dragonfly Mail Agent (dma) the default mta.
	    
	    dma accepts mail from a local Mail User Agent (MUA) and delivers it
	    locally or to a smarthost for delivery. dma does not accept inbound
	    mail (i.e., it does not listen on port 25) and is not intended to
	    provide the same functionality as a full MTA like postfix or sendmail.
	    It is intended for use cases such as delivering cron(8) mail. which
	    is the default configuration and usage of sendmail in the default
	    setup of the base system.
	    
	    In order to switch the default from sendmail to dma, we teach
	    mailwrapper to fallback on dma directly if the mailer.conf file cannot
	    be opened.
	    We install by default a mailer.conf file which points at dma
	    We install a mailer.conf file for sendmail in the examples.
	    
	    Relnotes:       yes
	    Differential Revision:  https://reviews.freebsd.org/D37035

But there are nothing pointers to be changed default MTA
changed to dma from sendmail ;-(  Especially people who
daily use sendmail with `service sendmail start', 
"Starting sendmail" message was shown but nothing done ;-)

There should be announced that default MTA is dma when
sendmail start ?

---
Kazuhiko Kiriyama