feat: add about us page.

demo/Ursa.Demo/Pages/AboutUsDemo.axaml.cs

@@ -0,0 +1,25 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using Ursa.Demo.ViewModels;
+
+namespace Ursa.Demo.Pages;
+
+public partial class AboutUsDemo : UserControl
+{
+    public AboutUsDemo()
+    {
+        InitializeComponent();
+    }
+    
+    protected override void OnLoaded(RoutedEventArgs e)
+    {
+        base.OnLoaded(e);
+        if (DataContext is AboutUsDemoViewModel vm)
+        {
+            var launcher = TopLevel.GetTopLevel(this)?.Launcher;
+            vm.Launcher = launcher;
+        }
+    }
+}