docs/zh_CN: Add dev-tools/kcov Chinese translation

Translate dev-tools/kcov into Chinese and add it in
dev-tools/zh_CN/index.rst.

Signed-off-by: Haoyang Liu <tttturtleruss@hust.edu.cn>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240421142021.19504-1-tttturtleruss@hust.edu.cn