feat(nextcloud): Add example

Signed-off-by: jld3103 <jld3103yt@gmail.com>

packages/nextcloud/example/example.dart

@@ -0,0 +1,13 @@
+import 'package:nextcloud/nextcloud.dart';
+import 'package:nextcloud/provisioning_api.dart';
+
+Future<void> main() async {
+  final client = NextcloudClient(
+    Uri.parse('http://localhost'),
+    loginName: 'admin',
+    password: 'admin',
+  );
+
+  final response = await client.provisioningApi.users.getCurrentUser();
+  print(response.body.ocs.data.id); // Will print `admin`
+}