Update detailed_global_legacy.cxx

Signed-off-by: PrecisEDAnon <[email protected]>

Author: PrecisEDAnon

src/dpl/src/optimization/detailed_global_legacy.cxx

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: BSD-3-Clause
 // Copyright (c) 2021-2025, The OpenROAD Authors
+// This file exists to preserve traditional DPO behavior and should at some point be merged with the newer DPO flow more cohesively.
 
 #include "detailed_global_legacy.h"