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

@@ -100,6 +100,11 @@ Devicetree
 * The :c:macro:`DT_ENUM_HAS_VALUE` and :c:macro:`DT_INST_ENUM_HAS_VALUE` macros are now
   checking all values, when used on an array, not just the first one.
 
+* 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
 ===