changed placeholders to text

lib/About.dart

@@ -5,6 +5,8 @@ class About extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return const Placeholder();
+    return const Center(
+      child: Text("About Page"),
+    );
   }
 }

lib/Links.dart

@@ -5,6 +5,8 @@ class Links extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return const Placeholder();
+    return const Center(
+      child: Text("Links Page"),
+    );
   }
 }

lib/Listen.dart

@@ -5,6 +5,8 @@ class Listen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return const Placeholder();
+    return const Center(
+      child: Text("Listen Page"),
+    );
   }
 }