Add Avalonia example project

Example.Avalonia/Program.cs

@@ -0,0 +1,22 @@
+using Avalonia;
+using DesktopNotifications.Avalonia;
+
+namespace Example.Avalonia
+{
+    internal class Program
+    {
+        public static void Main(string[] args)
+        {
+            BuildAvaloniaApp()
+                .StartWithClassicDesktopLifetime(args);
+        }
+
+        public static AppBuilder BuildAvaloniaApp()
+        {
+            return AppBuilder.Configure<App>()
+                .UsePlatformDetect()
+                .SetupDesktopNotifications()
+                .LogToTrace();
+        }
+    }
+}