l10n: zh_CN.po: 800+ new translations on command usages

Most of the 800+ new translations are contributed by Wang Sheng.
So he is a zh_CN l10n maintainer for Git now.

Also fixed translations for some terms, such as blob, dangling.

Signed-off-by: Wang Sheng <wangsheng2008love@163.com>
Signed-off-by: Jiang Xin <worldhello.net@gmail.com>