Update the iOS Xcode build requirements

(cherry picked from commit 7edcc413e80685d9dc2f8f4900b9e9403b4bb8ed)

docs/README-ios.md

@@ -4,7 +4,7 @@ iOS
 Building the Simple DirectMedia Layer for iOS 11.0+
 ==============================================================================
 
-Please note that building SDL requires at least Xcode 12.2 and the iOS 14.2 SDK.
+Please note that building SDL requires at least Xcode 16 and the iOS 18 SDK.
 
 Instructions: