update description (#1897)

diff --git a/lib/src/rules/always_require_non_null_named_parameters.dart b/lib/src/rules/always_require_non_null_named_parameters.dart
index 583a401..4849af0 100644
--- a/lib/src/rules/always_require_non_null_named_parameters.dart
+++ b/lib/src/rules/always_require_non_null_named_parameters.dart
@@ -9,7 +9,7 @@
 import '../analyzer.dart';
 import '../util/dart_type_utilities.dart';
 
-const _desc = r'Use @required.';
+const _desc = r'Specify `@required` on named parameters without defaults.';
 
 const _details = r'''