docs: clarify remote restrictions for git-upload-archive Commits ee27ca4 and 0f544ee introduced rules by which git-upload-archive would restrict clients from accessing unreachable objects. However, we never documented those rules anywhere, nor their reason for being. Let's do so now. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>