Update text about App Store policy

Author: jmagman

packages/image_picker/image_picker/README.md

@@ -23,6 +23,7 @@ As a result of implementing PHPicker it becomes impossible to pick HEIC images o
 Add the following keys to your _Info.plist_ file, located in `<project root>/ios/Runner/Info.plist`:
 
 * `NSPhotoLibraryUsageDescription` - describe why your app needs permission for the photo library. This is called _Privacy - Photo Library Usage Description_ in the visual editor.
+  * This permission will not be requested if you always pass `false` for `requestFullMetadata`, but App Store policy requires including the plist entry.
 * `NSCameraUsageDescription` - describe why your app needs access to the camera. This is called _Privacy - Camera Usage Description_ in the visual editor.
 * `NSMicrophoneUsageDescription` - describe why your app needs access to the microphone, if you intend to record videos. This is called _Privacy - Microphone Usage Description_ in the visual editor.