[bug-mailutils] add msglist examples to help

[Dan Jacobson]

$ mail
& help
this shows tons of "[msglist]" but no slight examples of a
msglist. Add some there please.

BTW, info says

        The "message list" in its simplest form is one of:
     ...
     Message range
          "Message range" is specified as two message numbers separated by a
          dash. It selects all messages with the number lying within that
          range.

However we can't use $ to represent the last message.  Same with
& d .-5
d: syntax error near 5
& d ^-9
d: syntax error near 9

P.S. In Info, at the end of the page it just says

   The following are the examples of valid message lists:

and stops.