[Support-mirrors] Documentation updated, and 2 gem/file mirrors now online

[Tom Copeland]

Hi all -

I just noticed that Austin's Gems seem to be sync'd up, so I've added
him to the RubyGem mirror rotation; now it's both Dennis and Auston for
both RubyGem and file mirrors:

http://rubyforge.org/credits/

Everyone else, as you have a chance, please contact Dennis with your
server info so he can push files your way.  Thanks much!

Also, I updated the "RubyForge Mirroring" document here:

http://rubyforge.org/docman/?group_id=5

to include information on the new architecture.
Comments/improvements/questions are welcome!

Thanks,

Tom