Docs/admin-guide/damon/sysfs: document 'LRU_PRIO' scheme action

This commit documents the 'lru_prio' scheme action for DAMON sysfs
interface.

Link: https://lkml.kernel.org/r/20220613192301.8817-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/admin-guide/mm/damon/usage.rst

@@ -264,6 +264,7 @@ that can be written to and read from the file and their meaning are as below.
  - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``
  - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``
  - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``
+ - ``lru_prio``: Prioritize the region on its LRU lists.
  - ``stat``: Do nothing but count the statistics
 
 schemes/<N>/access_pattern/