patchSubmittingPatches: advertise git-manpages-l10n project a bit

> The project takes our AsciiDoc sources of documentation and actively
> maintains the translations to various languages.
> 
> Let's give them enhanced visibility to help those who want to
> volunteer find them.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  Documentation/SubmittingPatches | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/SubmittingPatches b/Documentation/SubmittingPatches
> index c647c7e1b4..ff31049dce 100644
> --- a/Documentation/SubmittingPatches
> +++ b/Documentation/SubmittingPatches
> @@ -548,6 +548,13 @@ repositories.
>  
>  Patches to these parts should be based on their trees.
>  
> +- The "Git documentation translations" project, led by Jean-Noël
> +  Avila, translates our documentation pages.  Their work products are
> +  maintained separately from this project, not as part of our tree:
> +
> +	https://github.com/jnavila/git-manpages-l10n/
> +
> +
>  [[patch-flow]]
>  == An ideal patch flow
>