doc: Add a new migration guide entry

Bindings now use hyphens(-) instead of
underscores(_) as property separators.

Signed-off-by: James Roy <rruuaanng@outlook.com>

Author: rruuaanng

doc/releases/migration-guide-4.2.rst

@@ -97,6 +97,11 @@ Devicetree
   superfamily. Therefore, any dts files for boards that use Series 2 SoCs will need to change their
   include from ``#include <silabs/some_soc.dtsi>`` to ``#include <silabs/xg2[1-9]/some_soc.dtsi>``.
 
+* Property names in devicetree and bindings use hyphens(``-``) as separators, and replacing
+  all previously used underscores(``_``). For local code, you can migrate property names in
+  bindings to use hyphens by running the ``scripts/migrate_bindings_style.py`` script.
+
+
 DAI
 ===