commit/status: "git add <path>" is not necessarily how to resolve

commit/status: "git add <path>" is not necessarily how to resolve

When the desired resolution is to remove the path, "git rm <path>" is the
command the user needs to use.  Just like in "Changed but not updated"
section, suggest to use "git add/rm" as appropriate.

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