Refactor b.tar -> busybox.tar

The file was saved as busybox.tar, but the ls commands named it b.tar.

Docker-DCO-1.1-Signed-off-by: Steven Burgess <steven.a.burgess@hotmail.com> (github: stevenburgess)
Merge pull request #5832 from stevenburgess/documentation_cli_fix

Refactor b.tar -> busybox.tar