[bug-mailutils] Add debug example

[積丹尼 Dan Jacobson]

(info "(mailutils) debugging") is great, except without any examples, no
one will know how to debug.

Give an example of how to enhance
$ mail
to turn debugging on.

[Sergey Poznyakoff]

Post by 積丹尼 Dan Jacobson
(info "(mailutils) debugging") is great, except without any examples, no
one will know how to debug.
Give an example of how to enhance
$ mail
to turn debugging on.

OK. For the record: mail --debug-level=SPEC.

Regards,
Sergey