Perl 5.20 or later and Module::Build are required to build this module,
and IPC::Run is required to use it.  Either GnuPG v2 (version 2.1.12 or
later) or GnuPG v1 is also required.  The implementation of GnuPG can be
selected at runtime.  It has not been tested with versions of GnuPG older
than 1.4.23.

PGP::Sign requires the ability to redirect higher-numbered file
descriptors via IPC::Run, and thus will not work on Windows unless Perl is
built with some UNIX emulation layer that supports this.  It has also
never been tested with Gpg4win.
