MONGOID-5222 update error message

Author: neilshweky

lib/config/locales/en.yml

@@ -373,9 +373,10 @@ en:
           resolution: "Set the values from the parent, or redefine the association
             with only a single definition in the parent."
         invalid_value:
-          message: "The value %{value} cannot be written to a field of type %{field_class}"
-          summary: "The value %{value} could not be coerced to type %{field_class}"
-          resolution: "Verify that the value to be set corresponds to the field definition"
+          message: "The value %{value} cannot be written to a field of type %{field_class}."
+          summary: "The value %{value} could not be coerced to type %{field_class}."
+          resolution: "Verify that the value to be set corresponds to the field definition,
+            or turn off the Mongoid.validate_attribute_types flag to have nil written."
         mixed_relations:
           message: "Referencing a(n) %{embedded} document from the %{root}
             document via a non-embedded association is not allowed since the