docs/zh_CN: add cpu-freq index.rst translation

This patch translates Documention/cpu-freq/index.rst into Chinese.
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20210406070239.19910-5-siyanteng@loongson.cnSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/cpu-freq/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+.. include:: ../disclaimer-zh_CN.rst
+
+:Original: :doc:`../../../cpu-freq/index`
+:Translator: Yanteng Si <siyanteng@loongson.cn>
+
+.. _cn_index.rst:
+
+
+=======================================================
+Linux CPUFreq - Linux(TM)内核中的CPU频率和电压升降代码
+=======================================================
+
+Author: Dominik Brodowski  <linux@brodo.de>
+
+      时钟升降允许你在运行中改变CPU的时钟速度。这是一个很好的节省电池电量的方法，因为时
+      钟速度越低，CPU消耗的电量越少。
+
+
+.. toctree::
+   :maxdepth: 1
+
+   core
+   cpu-drivers
+   cpufreq-stats
+
+邮件列表
+------------
+这里有一个 CPU 频率变化的 CVS 提交和通用列表，您可以在这里报告bug、问题或提交补丁。要发
+布消息，请发送电子邮件到 linux-pm@vger.kernel.org。
+
+链接
+-----
+FTP档案:
+* ftp://ftp.linux.org.uk/pub/linux/cpufreq/
+
+如何访问CVS仓库:
+* http://cvs.arm.linux.org.uk/
+
+CPUFreq邮件列表:
+* http://vger.kernel.org/vger-lists.html#linux-pm
+
+SA-1100的时钟和电压标度:
+* http://www.lartmaker.nl/projects/scaling