Docs/mm/damon/design: document hugepage_size filter

'hugepage_size' DAMOS filter type is not documented on the design doc.
Add a description of the type.

Link: https://lkml.kernel.org/r/20250218223708.53437-3-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/mm/damon/design.rst

@@ -610,6 +610,9 @@ Below ``type`` of filters are currently supported.
     - Applied to pages that are accessed after the last access check from the
       scheme.
     - Handled by operations set layer.  Supported by only ``paddr`` set.
+- pages that managed in a given size range
+    - Applied to pages that managed in a given size range.
+    - Handled by operations set layer.  Supported by only ``paddr`` set.
 - address range
     - Applied to pages that belonging to a given address range.
     - Handled by the core logic.