doc: 增加默认焦点设置

Author: ArgoZhang

src/BootstrapBlazor.Server/Components/Routes.razor

@@ -1,5 +1,6 @@
 <Router AppAssembly="@typeof(Program).Assembly">
     <Found Context="routeData">
         <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
+        <FocusOnNavigate RouteData="routeData" Selector="h3" />
     </Found>
 </Router>