Docs/zh_CN: Translate index.rst to Simplified Chinese

Docs/zh_CN: Translate index.rst to Simplified Chinese

translate the "index.rst" into Simplified Chinese.

Update to commit e793b86ae44e("Documentation: networking: add
Twisted Pair Ethernet diagnostics at OSI Layer 1")

Signed-off-by: Wang Yaxin <wang.yaxin@zte.com.cn>
Signed-off-by: Jiang Kun <jiang.kun2@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: He Peilin <he.peilin@zte.com.cn>
Link: https://lore.kernel.org/r/20250319155110884FL0FcZmsjNzP1NnAC70Zs@zte.com.cn
Signed-off-by: Alex Shi <alexs@kernel.org>