fetch-pack: mention server version with verbose output

fetch-pack: mention server version with verbose output

Fetch-pack's verbose mode is more of a debugging mode (and
in fact takes two "-v" arguments to trigger via the
porcelain layer). Let's mention the server version as
another possible item of interest.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>