fix copy/paste mistake in README
use suitable kvm binary depending on OS & arch

Debian-based systems no longer have /usr/bin/qemu-kvm since
qemu 1.3.0. This patch adds possible binary paths to a list
and will pass the 1st one found to the libvirt template.

See http://anonscm.debian.org/gitweb/?p=pkg-qemu/qemu.git;f=debian/qemu-kvm.NEWS;hb=debian-experimental
add Debian/Ubuntu notes to README
Merge pull request #1 from mfournier/debian-fixup

Debian fixup