As an option to the "diff" family, it is fairly obvious what
"detect renames" means. However, for revision traversal, the
"-M" option is just included in the long list of options,
with no indication that it is about showing renames in diffs
versus following renames. Let's make it more explicit.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>