Docs/admin-guide/mm/damon/usage: update stats update process for refresh_ms

Docs/admin-guide/mm/damon/usage: update stats update process for refresh_ms

DAMOS stats on sysfs was only manually updated.  Recent addition of
'refresh_ms' knob enabled periodic and automated updates of the stats.
The document for stats update process is not updated for the change,
however.  Update.

Link: https://lkml.kernel.org/r/20260118180305.70023-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
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>