git-config: fix misworded --type=path explanation

git-config: fix misworded --type=path explanation

When `--type=<type>` was added as a prefered alias for `--<type>` by
fb0dc3bac1 (builtin/config.c: support `--type=<type>` as preferred
alias for `--<type>`), the explanation for the path type was
reworded.  Whereas the previous explanation said "expand a leading
`~`" this was changed to "adding a leading `~`".  Change "adding" to
"expanding" to correctly explain the canonicalization.

Signed-off-by: Evan Gates <evan.gates@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>