add --to example.

積丹尼 Dan Jacobson <[email protected]> Tue, 11 Jan 2022 20:29:11 +0800

Newsgroups	gmane.comp.gnu.mailutils.bugs
Message-ID	<[email protected]>

(info "(mailutils) Invoking Mail") says
   '-t'
   '--to'
        Read recipients from the message header.  Ignore addresses listed
        in the command line.

All I know is that will cause FILE to be ignored when using
$ cat FILE | mail.mailutils --to ... ...

Therefore please add an examples.