docs: fix filter-branch example for quoted paths
docs: fix filter-branch example for quoted paths

If there is a quoted path, update-index will correctly
unquote it. However, we must take care to put our new prefix
inside the double-quote.

Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git