Explain why a subset of util-linux is extracted

This adds a copy of the explanation from TJMCS about why only a
subset of the `util-linux` package is installed, as per #45, so that
the next engineer along doesn't wonder at that.
This change should fix issue 297 on the Razor issue list
Merge pull request #56 from tjmcs/tb/fixes_razor_issue_297

Fixes Razor issue 297; MK now uses 'lshw -disable dmi' under kvm