docs: dt: writing-schema: Document preferred order of properties

Document established Devicetree bindings maintainers review practice:
using DTS coding style property order in both 'properties' and
'required' secions.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250713-dt-bindings-docs-v2-4-672c898054ae@linaro.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Author: krzk

Documentation/devicetree/bindings/writing-schema.rst

@@ -171,6 +171,9 @@ Coding style
 Use YAML coding style (two-space indentation). For DTS examples in the schema,
 preferred is four-space indentation.
 
+Place entries in 'properties' and 'required' sections in the same order, using
+style from Documentation/devicetree/bindings/dts-coding-style.rst.
+
 Testing
 -------