Replace placeholder with a basic message for now.

lib/pages/settings.dart

@@ -13,6 +13,10 @@ class SettingsPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Placeholder();
+    return Center(
+      child: Text(
+        "No settings yet. :)",
+      ),
+    );
   }
 }