docs/zh_CN: add vm page_migration translation

Translate .../vm/page_migration.rst into Chinese.
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/44bc4486e5019f689bcbec20a629a9f7800ece33.1654585011.git.siyanteng@loongson.cnSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/translations/zh_CN/vm/index.rst

@@ -51,6 +51,7 @@ Linux内存管理文档
    numa
    overcommit-accounting
    page_frags
+   page_migration
    page_owner
    page_table_check
    remap_file_pages
@@ -62,7 +63,6 @@ TODOLIST:
 * arch_pgtable_helpers
 * free_page_reporting
 * hugetlbfs_reserv
-* page_migration
 * slub
 * transhuge
 * unevictable-lru