docs: Belatedly update for move of qmp-commands.txt
Missed in commit d076a2a and commit bd6092e.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1474546563-16332-1-git-send-email-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>