docs/zh_CN: add core-api assoc_array translation

Translate Documentation/core-api/assoc_array.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/860ac85d9a2a83c2b63eb8d1be929ad64280d7b2.1634358018.git.siyanteng@loongson.cn


Signed-off-by: Jonathan Corbet <corbet@lwn.net>