git-reset.txt: render tables correctly under Asciidoctor

git-reset.txt: render tables correctly under Asciidoctor

Asciidoctor removes the indentation of each line in these tables, so the
last lines of each table have a completely broken alignment.

Similar to 379805051d ("Documentation: render revisions correctly under
Asciidoctor", 2018-05-06), use an explicit literal block to indicate
that we want to keep the leading whitespace in the tables.

Because this gives us some extra indentation, we can remove the one that
we have been carrying explicitly. That is, drop the first six spaces of
indentation on each line. With Asciidoc (8.6.10), this results in
identical rendering before and after this commit, both for git-reset.1
and git-reset.html.

Reported-by: Paweł Samoraj <samoraj.pawel@gmail.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>