docs: Add version{added,changed} notes to the hw_machine_type guide
docs: Add version{added,changed} notes to the hw_machine_type guide

These were missed in the original change but add some useful context to
readers of when things have been changed.

blueprint: libvirt-default-machine-type
Change-Id: I64ef0efc80a088385c9ac45a818cc807490d2de1

mahak/nova,mahak/nova,openstack/nova,openstack/nova,mahak/nova,openstack/nova