Add a test directory to point users to the correct tests inside the example directory.

Author: ditman

packages/url_launcher/url_launcher_web/test/README.md

@@ -0,0 +1,5 @@
+## test
+
+This package uses integration tests for testing.
+
+See `example/README.md` for more info.

packages/url_launcher/url_launcher_web/test/tests_exist_elsewhere_test.dart

@@ -0,0 +1,10 @@
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('Tell the user where to find the real tests', () {
+    print('---');
+    print('This package uses integration_test for its tests.');
+    print('See `example/README.md` for more info.');
+    print('---');
+  });
+}