doc/ls-remote: cosmetic cleanups for examples

doc/ls-remote: cosmetic cleanups for examples

There are effectively three example commands and their output, but
they're smushed together with no extra whitespace. Let's add some blank
lines to make them more readable.

Likewise, the first example uses "./." to refer to the path of the
current repository, which is somewhat distracting. That may have been
necessary back in 2005 when it was added, but we can just say "." these
days.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>