fetch: document that pruning happens before fetching This was changed in 10a6cc8 (fetch --prune: Run prune before fetching, 2014-01-02), but it seems that nobody in that discussion realized we were advertising the "after" explicitly. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>