v4merge-strategies.adoc: detail submodule merge

>
> Submodule merges are, in general, similar to other merges based on oid
> three-way-merge. When a conflict happens, however, Git has two special
> cases (introduced in 68d03e4a6e44) on handling the conflict before
> yielding it to the user. From the merge-ort and merge-recursive sources:
>
> - "Case #1: a is contained in b or vice versa": both strategies try to
> perform a fast-forward in the submodules if the commit referred by the
> conflicted submodule is descendant of another;
>
> - "Case #2: There are one or more merges that contain a and b in the
> submodule.  If there is only one, then present it as a suggestion to the
> user, but leave it marked unmerged so the user needs to confirm the
> resolution."
>
> Add a small paragraph on merge-strategies.adoc describing this behavior.
>
> Helped-by: Junio C Hamano <gitster@pobox.com>
> Helped-by: Elijah Newren <newren@gmail.com>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>
> Just removing an extra blank line from v3.
>
> Documentation/merge-strategies.adoc | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/Documentation/merge-strategies.adoc b/Documentation/merge-strategies.adoc
> index 5fc54ec060..c8d81bcda6 100644
> --- a/Documentation/merge-strategies.adoc
> +++ b/Documentation/merge-strategies.adoc
> @@ -22,6 +22,13 @@ ort::
>         was written as a replacement for the previous default
>         algorithm, `recursive`.
>  +
> +In the case where the path is a submodule, if the submodule commit used on
> +one side of the merge is a descendant of the submodule commit used on the
> +other side of the merge, Git attempts to fast-forward to the
> +descendant. Otherwise, Git will treat this case as a conflict, suggesting
> +as a resolution a submodule commit that is descendant of the conflicting
> +ones, if one exists.
> ++
>  The 'ort' strategy can take the following options:
>
>  ours;;
> @@ -96,6 +103,9 @@ recursive::
>         the default strategy for resolving two heads from Git v0.99.9k
>         until v2.33.0.
>  +
> +For a path that is a submodule, the same caution as 'ort' applies to this
> +strategy.
> ++
>  The 'recursive' strategy takes the same options as 'ort'.  However,
>  there are three additional options that 'ort' ignores (not documented
>  above) that are potentially useful with the 'recursive' strategy:
> --
> 2.39.5 (Apple Git-154)