docs/zh_CN: fix link issue in howto.rst

Now we could follow links in created html files.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Harry Wei <harryxiyou@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Federico Vaga <federico.vaga@vaga.pv.it>
Cc: SeongJae Park <sj38.park@gmail.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>