The 0.7 version was just an example, but since we're on 0.9 now,
updating the number cannot be wrong. The new admonition helps KVM users
to configure debootstrap correctly so that instances can be shutdown
cleanly.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>