[bug-mailutils] imap: folder instructions

[積丹尼 Dan Jacobson]

$ mail --file imaps://...
Please document how to get a list of available folders at this point.
Add it to (info "(mailutils) Changing mailbox/directory")

Also add an example of how to use "fold" when using imaps://...
Just saying
? fold SPAM
will refer to a local folder, so one probably needs a very long
? fold imaps://....

Also mention how to get there from the start on (info "(mailutils) Remote 
Mailboxes"). My guess
$ mail -f imaps://...\;folder=SPAM
didn't work.

Also mention that one needs %40 instead of @ in the USER part of
imaps://, if you haven't already.

Thanks.