Add new translations

* Documentation/translations/zh_CN/kernel-hacking/index.rst
* Documentation/translations/zh_CN/kernel-hacking/hacking.rst

And link them to zh_CN/index.rst.
Signed-off-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Link: https://lore.kernel.org/r/20210323091651.GA23904@mipcSigned-off-by: Jonathan Corbet <corbet@lwn.net>