Add [verse] to the SYNOPSIS section of git-submodule.txt.

Add [verse] to the SYNOPSIS section of git-submodule.txt.

The SYNOPSIS section of git-submodule.txt contains two forms.  Since
it doesn't use the verse style, the line boundary between them is not
preserved and the second form can appear on the same line as the first
form.  Adding [verse] enables the verse style, which preserves the
line boundary between them.

Signed-off-by: Matt Kraai <kraai@ftbfs.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>