Add note about the PATCH method

Author: bicpi

reference/forms/types/options/method.rst.inc

@@ -23,3 +23,9 @@ used to decide whether to process the form submission in the
     render a ``_method`` hidden field in your form. This is used to "fake"
     these HTTP methods, as they're not supported on standard browsers. For
     more information, see :doc:`/cookbook/routing/method_parameters`.
+
+.. note:
+
+    Only the PATCH method allows submitting partial data without that missing
+    fields are set to ``null`` in the underlying data (preserving default
+    values, if any).