Docs/admin-guide/mm/damon/lru_sort: document filter_young_pages

Docs/admin-guide/mm/damon/lru_sort: document filter_young_pages

Document the new DAMON_LRU_SORT parameter, filter_young_pages.  It can be
used to use page level access re-check for the LRU sorting.

Link: https://lkml.kernel.org/r/20260113152717.70459-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: wang lian <lianux.mm@gmail.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>