Direct users to sign up for Nextcloud if they don't have one

app/lib/help_utils.dart

@@ -14,3 +14,5 @@ const editPhotosUrl = "https://bit.ly/3v82oKA";
 const collectionTypesUrl = "https://bit.ly/3OwSiNq";
 const contributorsUrl = "https://bit.ly/3QhlQQs";
 const videoPreviewUrl = "https://bit.ly/4c7cazP";
+
+const nextcloudProviderUrl = "https://bit.ly/3xIzgL7";

app/lib/widget/sign_in.dart

@@ -12,9 +12,11 @@ import 'package:nc_photos/db/entity_converter.dart';
 import 'package:nc_photos/entity/pref.dart';
 import 'package:nc_photos/entity/pref_util.dart' as pref_util;
 import 'package:nc_photos/exception_event.dart';
+import 'package:nc_photos/help_utils.dart' as help_util;
 import 'package:nc_photos/legacy/connect.dart' as legacy;
 import 'package:nc_photos/snack_bar_manager.dart';
 import 'package:nc_photos/theme.dart';
+import 'package:nc_photos/url_launcher_util.dart';
 import 'package:nc_photos/widget/app_intermediate_circular_progress_indicator.dart';
 import 'package:nc_photos/widget/connect.dart';
 import 'package:nc_photos/widget/expandable_container.dart';

app/lib/widget/sign_in/view.dart

@@ -117,7 +117,12 @@ class _BodyState extends State<_Body> {
                             .cancelButtonLabel),
                       )
                     else
-                      Container(),
+                      TextButton(
+                        onPressed: () {
+                          launch(help_util.nextcloudProviderUrl);
+                        },
+                        child: const Text("DON'T HAVE ONE?"),
+                      ),
                     ElevatedButton(
                       onPressed: () {
                         if (_formKey.currentState?.validate() == true) {