mm/page_owner: update Documentation with 'show_handles' and 'show_stacks_handles'

mm/page_owner: update Documentation with 'show_handles' and 'show_stacks_handles'

Describe and provide examples for 'show_handles' and 'show_stacks_handles'.

Link: https://lkml.kernel.org/r/20251001175611.575861-6-mfo@igalia.com
Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>