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>