Host the l10n coordinator repository in a dedicated github organization
account "git-l10n", so that the team may have a more permanent home.
Also add a hint about reference of TEAMS file for l10n contributors.

Update TEAMS file with new zh_CN l10n team members and a repository URL.
Signed-off-by: NJiang Xin <worldhello.net@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>