docs/zh_CN: translate kernel enforcement statement

kernel enforcement statement is a important statement to show a kind of
attitude in kernel community. This patch translate it into Chinese and
add it into toctree.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Harry Wei <harryxiyou@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: https://lore.kernel.org/r/1576811085-30544-3-git-send-email-alex.shi@linux.alibaba.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>