[packagekit] Document about portage backend

[Mounir Lamouri]

Hi,

As some people may know, I've began the portage backend in the context
of my Google Summer of Code and I've wrote a document about this work:
where it has been, the difficulties, what should be done in the
future, etc.

That's pretty Gentoo/portage oriented however, you may found a few
interesting stuff:
http://dev.gentoo.org/~volkmar/post-gsoc-packagekit-portage.html

Thanks,
Mounir