Docs/admin-guide/mm/damon/usage: move debugfs intro to the bottom of the section

Docs/admin-guide/mm/damon/usage: move debugfs intro to the bottom of the section

On the DAMON usage introduction section, the introduction of DAMON
debugfs interface, which is deprecated, is above kernel API, which is
actively supported.  Move the DAMON debugfs intro to bottom, so that
readers have less chances to read it.

Link: https://lkml.kernel.org/r/20230907022929.91361-4-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>