[DispatcherQueueExtensions] Document how to install & consume these methods

docs/windows/Extensions/DispatcherQueueExtensions.md

@@ -16,11 +16,22 @@ icon: Assets/Extensions.png
 
 The `DispatcherQueueExtensions` type provides a collection of extensions methods for [`DispatcherQueue`](/uwp/api/windows.system.dispatcherqueue) objects that makes it easier to execute code on a specific UI thread. A `DispatcherQueue` instance can be retrieved and cached for later use, and then used through any of the available helper methods to dispatch a delegate invocation on it.
 
+## Setup
+
+First, add the [`CommunityToolkit.WinUI.Extensions`](https://www.nuget.org/packages/CommunityToolkit.WinUI.Extensions) to your project. See [Get started](../getting-started.md). Then:
+
+```csharp
+// Imports the extension methods
+using CommunityToolkit.WinUI;
+```
+
 ## Syntax
 
 The `DispatcherQueueExtensions` type exposes a number of overloads of its `EnqueueAsync` method to dispatch either synchronous or asynchronous delegates, and to optionally have them return a value that is then relayed back to the caller through an awaitable task. Here are some examples of how these extension methods can be used:
 
 ```csharp
+using CommunityToolkit.WinUI;
+
 // Get a DispatcherQueue instance for later use. This has to be called on the UI thread,
 // but it can then be cached for later use and accessed from a background thread as well.
 DispatcherQueue dispatcherQueue = DispatcherQueue.GetForCurrentThread();