Update main-window.mdx (docs/get-started/test-drive/main-window#the-mainwindow-content) (#635)

* Update main-window.mdx

MainViewModel -> MainWindowViewModel

* Update main-window.mdx

* Update main-window.mdx

Author: 0xf0pfp183

docs/get-started/test-drive/main-window.mdx

@@ -30,6 +30,14 @@ Inside the Windows Content, you will see a `<TextBlock>...</TextBlock>` XAML tag
 `Text` to the screen. The `Text` property of the `TextBlock` is bound to the **Greeting** property of 
 the **MainViewModel** class.
 
+:::note
+The class name may appear as either:  
+- `MainViewModel`  
+- `MainWindowViewModel`  
+
+Check which template your project uses to confirm the correct name.  
+:::
+
 ```xml title='XAML'
 <TextBlock Text="{Binding Greeting}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
 ```