docs/zh_CN: add core-api workqueue.rst translation

This patch translates Documentation/core-api/workqueue.rst into Chinese.
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20210517132927.3461185-1-siyanteng@loongson.cnSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/core-api/index.rst

@@ -25,9 +25,9 @@
    kernel-api
    printk-basics
    printk-formats
+   workqueue
 
 Todolist:
-   workqueue
    symbol-namespaces
 
 数据结构和低级实用程序