[Gm2] updated documentation with additional info on prerequisites

[Gaius Mulley]

Hi,

as there have been a few queries on prerequisites I've updated the gm2
build documentation and added a new section:

  http://nongnu.org/gm2/prerequisites.html

hope this helps - would be interesting to hear from people on non debian
systems whether this improves building success,

regards,
Gaius