git-cat-file.txt: fix list continuations rendering literally

git-cat-file.txt: fix list continuations rendering literally

With Asciidoctor, all of the '+' introduced in a797c0ea04 ("cat-file:
add mailmap support to --batch-check option", 2022-12-20) render
literally rather than functioning as list continuations. With asciidoc,
this renders just fine. It's not too surprising that there is room for
ambiguity and surprises here, since we have lists within lists.

Simply replacing all of these '+' with empty lines makes this render
fine using both tools. Except, in the third hunk, where after this inner
'*' list ends, we want to continue with more contents of the outer list
item (`--batch-command=<format>`). We can solve any ambiguity here and
make this clear to both tools by wrapping the inner list in an open
block (using "--").

For consistency, let's wrap all three of these inner lists from
a797c0ea04 in open blocks. This also future-proofs us a little -- if we
ever gain more contents after any of those first two lists, as we did
already in a797c0ea04 for the third list, we're prepared and should
render fine with both asciidoc and Asciidoctor from the start.

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