docs/zh_CN: add vm frontswap translation

Translate .../vm/_free_page_reporting.rst into Chinese.
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/vm/index.rst

@@ -27,11 +27,11 @@ TODO:待引用文档集被翻译完毕后请及时修改此处）
    free_page_reporting
    highmem
    ksm
+   frontswap
 
 TODOLIST:
 * arch_pgtable_helpers
 * free_page_reporting
-* frontswap
 * hmm
 * hwpoison
 * hugetlbfs_reserv