[PATCH] doc: Note pinentry-mode for passphrase opts

[Daniel Kahn Gillmor]

On Mon 2018-01-08 19:19:17 +0100, Andre Heinecke wrote:

> The pinentry-mode should be mentioned in my opinion in the doc / manpage of 
> the passphrase options because they won't work if the pinentry-mode is not set 
> to loopback. This is similar to the already mentioned --batch requirement.

I agree with the sentiment behind this change.  however, some of the
wording can be improved:

>  Note that this passphrase is only used if the option @option{--batch}
> -has also been given.  This is different from GnuPG version 1.x.
> +has also been given and @option{--pinentry-mode} has to be set to @code{loopback}.
> +This is different from GnuPG version 1.x and 2.0.x.

this should say something like "the requirement for loopback mode was
introduced in GnuPG version 2.1.$whatever". That makes it clearer and
less ambiguous to people who are trying to understand how to configure a
bunch of systems with different versions installed.

      --dkg