Bug#813833: -fork option missing in manpage

[Yvan Masson]

Package: john
Version: 1.7.8-1
Version: 1.8.0-2

Dear maintainer,

Could you add to the manpage the "-fork" option ? Currently, it is only
briefly described in /usr/share/doc/john/FAQ.gz.

Thanks for you time and work,
Yvan