Add notes for MacOS, since this API is unified.

docs/ios/platform/user-notifications/enhanced-user-notifications.md

@@ -107,6 +107,7 @@ The new User Notification framework provides a unified notification API across t
 - **iOS** - Full support to manage and schedule notifications.
 - **tvOS** - Adds the ability to badge app icons for local and remote notifications.
 - **watchOS** - Adds the ability to forward notifications from the user's paired iOS device to their Apple Watch and gives watch apps the ability to do local notifications directly on the watch itself.
+- **macOS** - Full support to manage and schedule notifications.
 
 For more information, please see Apple's [UserNotifications Framework Reference](https://developer.apple.com/reference/usernotifications) and [UserNotificationsUI](https://developer.apple.com/reference/usernotificationsui) documentation.
 
@@ -124,21 +125,47 @@ Additionally, these approval levels must be requested and set for both local and
 
 Notification permission should be requested as soon as the app launches by adding the following code to the `FinishedLaunching` method of the `AppDelegate` and setting the desired notification type (`UNAuthorizationOptions`):
 
+> [!NOTE]
+> `UNUserNotificationCenter` is only available from iOS 10+. Therefore, it's best practice to check the macOS version before sending the request. 
+
 ```csharp
 using UserNotifications;
 ...
 
 public override bool FinishedLaunching (UIApplication application, NSDictionary launchOptions)
 {
-    // Request notification permissions from the user
-    UNUserNotificationCenter.Current.RequestAuthorization (UNAuthorizationOptions.Alert, (approved, err) => {
-        // Handle approval
-    });
+    // Version check
+    if (UIDevice.CurrentDevice.CheckSystemVersion (10, 0)) {
+        // Request notification permissions from the user
+        UNUserNotificationCenter.Current.RequestAuthorization (UNAuthorizationOptions.Alert, (approved, err) => {
+            // Handle approval
+        });
+    }
 
     return true;
 }
 ```
 
+As this API is unified and also works on Mac 10.14+, if you are targetting macOS you must also check for the Notification permission as soon as possible:
+
+```csharp
+using UserNotifications;
+...
+
+public override void DidFinishLaunching (NSNotification notification)
+{
+    // Check we're at least v10.14
+    if (NSProcessInfo.ProcessInfo.IsOperatingSystemAtLeastVersion (new NSOperatingSystemVersion (10, 14, 0))) {
+        // Request notification permissions from the user
+        UNUserNotificationCenter.Current.RequestAuthorization (UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound, (approved, err) => {
+            // Handle approval
+        });
+    }
+}
+
+> [!NOTE]
+> With MacOS apps, for the permission dialog to appear, you must sign your macOS app, even if building locally in DEBUG mode. Therefore, **Project->Options->Mac Signing->Sign the application bundle** must be checked.
+
 Additionally, a user can always change the notification privileges for an app at any time using the **Settings** app on the device. The app should check for the user's requested notification privileges before presenting a notification using the following code:
 
 ```csharp
@@ -667,4 +694,4 @@ This article has covered all of the ways that Users Notification have been enhan
 - [iOS 10 Samples](/samples/browse/?products=xamarin&term=Xamarin.iOS%2biOS10)
 - [UserNotifications Framework Reference](https://developer.apple.com/reference/usernotifications)
 - [UserNotificationsUI](https://developer.apple.com/reference/usernotificationsui)
-- [Local and Remote Notification Programming Guide](https://developer.apple.com/documentation/usernotifications)
+- [Local and Remote Notification Programming Guide](https://developer.apple.com/documentation/usernotifications)