Update README.md (p2#355)

Author: Lindemann

README.md

@@ -123,6 +123,16 @@ func application(_ app: UIApplication,
 }
 ```
 
+For iOS 13 make the callback in `SceneDelegate.swift`
+
+```swift
+func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {
+	if let url = URLContexts.first?.url {
+		AppDelegate.shared.oauth2?.handleRedirectURL(url)
+	}
+}
+```
+
 You’re all set!
 
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