docs/zh_CN: add openrisc index.rst translation

This patch translates Documentation/openrisc/index.rst into Chinese.
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/f3878525e0d5f94a9c541f5ec8fd31b44a6dc5cd.1618568135.git.siyanteng@loongson.cnSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/openrisc/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+.. include:: ../disclaimer-zh_CN.rst
+
+:Original: :doc:`../../../openrisc/index`
+:Translator: Yanteng Si <siyanteng@loongson.cn>
+
+.. _cn_openrisc_index:
+
+
+=================
+OpenRISC 体系架构
+=================
+
+.. toctree::
+   :maxdepth: 2
+
+   openrisc_port
+   todo
+
+Todolist:
+    features
+
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`