Update to webpage

[Fred Kiefer]

The main link for GNUstep installation on our wiki leads to this page:

http://www.gnustep.org/resources/documentation/User/GNUstep/gnustep-howto_toc.html

It is from 2008 and partly outdated. It also misses all the sub-sections
of section 6, which would be the machine specific instructions. Most
likely somebody manually changed the page
http://www.gnustep.org/resources/documentation/User/GNUstep/gnustep-howto_6.html
but forgot to update the index page as well.

Could somebody please update the index as well? I think this document
should be generated from a file in GNUstep make.

Thank you
Fred