docs(iOS): Update docs for animationDuration in 6.x

Author: kmichalikk

versioned_docs/version-6.x/native-stack-navigator.md

@@ -591,7 +591,7 @@ Only supported on iOS.
 
 Changes the duration (in milliseconds) of `slide_from_bottom`, `fade_from_bottom`, `fade` and `simple_push` transitions on iOS. Defaults to `350`.
 
-The duration of `default` and `flip` transitions isn't customizable.
+For screens with `default` and `flip` transitions, and for screens with `presentation` set to `modal`, `formSheet`, `pageSheet` (regardless of transition), the duration isn't customizable.
 
 Only supported on iOS.