Augment ino64 entry

When updating across this change (the introduction of ino64), the
"fast and loose" practice of rebooting to multiuser and then doing an
installworld fails with missing symbols. Recommend strongly that users
do this in single user mode. The multiuser case only ever works by
accident because its requirements are stronger than is supported
accross this change. It usually works because critical symbols don't
change their version number in libc, which wasn't the case here.