patchdoc/ls-files: put nested list for "-t" option into block

> We could fix it by adding a "+" before the sub-list to connect it to the
> rest of the "-t" text. But using a pair of "--" to delimit the block is
> perhaps more readable, and may have better compatibility with
> asciidoctor, as in 39a869b2f2 (Documentation/rev-list-options: wrap
> --date=<format> block with "--", 2019-03-30).

>  Documentation/git-ls-files.txt | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
> index 5298f1bc30..8461c0e83e 100644
> --- a/Documentation/git-ls-files.txt
> +++ b/Documentation/git-ls-files.txt
> @@ -118,6 +118,7 @@ OPTIONS
>  	linkgit:git-status[1] `--short` or linkgit:git-diff[1]
>  	`--name-status` for more user-friendly alternatives.
>  +
> +--
>  This option identifies the file status with the following tags (followed by
>  a space) at the start of each line:
>  
> @@ -128,6 +129,7 @@ a space) at the start of each line:
>  	C::	modified/changed
>  	K::	to be killed
>  	?::	other
> +--
>  
>  -v::
>  	Similar to `-t`, but use lowercase letters for files

> The description for the "-t" option contains a sub-list of all of the
> possible file status outputs. But because of the newline separating that
> list from the description paragraph, asciidoc treats the sub-list
> entries as a continuation of the overall options list, rather than as
> children of the "-t" description.
> 
> We could fix it by adding a "+" before the sub-list to connect it to the
> rest of the "-t" text. But using a pair of "--" to delimit the block is
> perhaps more readable, and may have better compatibility with
> asciidoctor, as in 39a869b2f2 (Documentation/rev-list-options: wrap
> --date=<format> block with "--", 2019-03-30).
> 
> The extra blank line comes from 5bc0e247c4 (Document ls-files -t as
> semi-obsolete., 2010-07-28), but the problem actually seems older than
> that. Before then, we did:
> 
>   -t:: some text...
>     H:: cached
>     M:: unmerged
>     etc...
> 
> but asciidoc also treats that as one big list. So this problem seems to
> have been around forever.
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
> Junio: I happened to notice this while hunting for "ls-files" options
>        that could make your makefile de-dup patch unnecessary (but
>        didn't find anything).
> 
> Todd: Just an FYI that your "--" strategy is spreading. :)