Update Basic-Theme documentation

docs/en/UI/Blazor/Basic-Theme.md

@@ -85,6 +85,27 @@ You can simply override the styles in the Global Styles file of your application
 
 See the [Customization / Overriding Components](Customization-Overriding-Components.md) to learn how you can replace components, customize and extend the user interface.
 
+### Overriding the Menu Item
+Basic theme supports overriding a single menu item with a custom component. You can create a custom component and call `UseComponent` extension method of Basic Theme in the **MenuContributor**.
+
+```csharp
+using Volo.Abp.AspNetCore.Components.Web.BasicTheme.Navigation;
+
+//...
+
+context.Menu.Items.Add(
+  new ApplicationMenuItem("Custom.1", "My Custom Menu", "#")
+    .UseComponent(typeof(MyMenuItemComponent)));
+```
+
+```html
+<li class="nav-item">
+    <a href="#" class="nav-link">
+        My Custom Menu
+    </a>
+</li>
+```
+
 ### Copy & Customize
 
 You can run the following [ABP CLI](../../CLI.md) command in **Blazor{{if UI == "Blazor"}}WebAssembly{{else}} Server{{end}}** project directory to copy the source code to your solution: