doc/clone: Pick more compelling paths for the --reference example

There may be times when using one of your local repositories as a reference for a new clone make sense, but the implied version-bump in the old example isn't one of them. I think a more intuitive example is multi-user system with a central reference clone, and the new paths hint at this use case. Signed-off-by: W. Trevor King <wking@tremily.us> Signed-off-by: Junio C Hamano <gitster@pobox.com>