doc/zh_CN: fix title heading markup in admin-guide cpu-load

Documentation generation warns:

  Documentation/translations/zh_CN/admin-guide/cpu-load.rst:1:
  WARNING: Title overline too short.

Extend title heading markup by one. It was just off by one.

Fixes: e210c66 ("doc/zh_CN: add cpu-load Chinese version")
Signed-off-by: Lukas Bulwahn <[email protected]>
Acked-by: Tao Zhou <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

Author: bulwahn

Documentation/translations/zh_CN/admin-guide/cpu-load.rst

@@ -1,6 +1,6 @@
-=======
+========
 CPU 负载
-=======
+========
 
 Linux通过``/proc/stat``和``/proc/uptime``导出各种信息，用户空间工具
 如top(1)使用这些信息计算系统花费在某个特定状态的平均时间。