gitcli: contrast wildcard given to shell and to git

gitcli: contrast wildcard given to shell and to git

People who are not used to working with shell may intellectually
understand how the command line argument is massaged by the shell
but still have a hard time visualizing the difference between
letting the shell expand fileglobs and having Git see the fileglob
to use as a pathspec.

Signed-off-by: Junio C Hamano <gitster@pobox.com>