wkd: Add option --directory to the server.
* tools/gpg-wks-server.c (opts): Add '--directory', (main): Explain how to set correct permissions. (command_list_domains): Create an empty policy file and remove the warning for an empty policy file.
Note that a policy file is meanwhile required and thus is is useful to
create it.
- Signed-off-by: Werner Koch <wk@gnupg.org>