Docs/admin-guide/mm/damon/usage: place debugfs usage at the bottom

debugfs interface is deprecated.  Put it at the bottom of the document
so that readers have less chances to read it.

Link: https://lkml.kernel.org/r/20230907022929.91361-3-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>