feat: add sample in web app.

demo/Semi.Avalonia.Demo.Web/Program.cs

@@ -0,0 +1,26 @@
+using System.Runtime.Versioning;
+using Avalonia;
+using Avalonia.Media;
+using Avalonia.Web;
+using Semi.Avalonia.Demo.Web;
+
+[assembly: SupportedOSPlatform("browser")]
+
+internal partial class Program
+{
+    private static void Main(string[] args) => BuildAvaloniaApp()
+        .With(new FontManagerOptions
+        {
+            FontFallbacks = new[]
+            {
+                new FontFallback
+                {
+                    FontFamily = new FontFamily("avares://Semi.Avalonia.Demo.Web/Assets/SourceHanSansCN-Regular.otf#Source Han Sans CN")
+                }
+            }
+        })
+        .SetupBrowserApp("out");
+
+    public static AppBuilder BuildAvaloniaApp()
+        => AppBuilder.Configure<App>();
+}