[darwinbuild] Building Darwin Projects

I've posted a document that describes the Apple build environment. Hopefully this will give a little insight into what darwinbuild is doing when building a project. <http://opendarwin.org/projects/darwinbuild/doc/build/index.html> I'll follow up soon with a corresponding page about darwinbuild usage, and a new darwinbuild release to fix the issues that have been reported recently. - Kevin