Comment 1 for bug 1911440

I guess the way it's done might be a bit confusing at first, since not sure if it will be completely obvious from first glance that not the vendored minilzo is used but instead the sources are overwritten via debian/rules. Maybe a mention in README.source could be useful. On the other hand, I think stuff in grub2 is already very confusing so oh well. Let's just proceed!