docs/zh_CN: add openrisc translation to zh_CN index

This patch add zh_CN/openrisc to zh_CN/index.
Signed-off-by: NYanteng Si <siyanteng@loongson.cn>
Reviewed-by: NWu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/162fb50638028c9b0a92a0ce5c53e691be0cfec2.1618568135.git.siyanteng@loongson.cnSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/index.rst

@@ -29,6 +29,7 @@
    iio/index
    riscv/index
    core-api/index
+   openrisc/index
 
 目录和表格
 ----------