fastlane supply basic scaffold

frontend/ios/fastlane/screenshots/README.txt

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+## Screenshots Naming Rules
+
+Put all screenshots you want to use inside the folder of its language (e.g. `en-US`).
+The device type will automatically be recognized using the image resolution.
+
+The screenshots can be named whatever you want, but keep in mind they are sorted
+alphabetically, in a human-friendly way. See https://github.com/fastlane/fastlane/pull/18200 for more details.
+
+### Exceptions
+
+#### iPad Pro (3rd Gen) 12.9"
+
+Since iPad Pro (3rd Gen) 12.9" and iPad Pro (2nd Gen) 12.9" have the same image
+resolution, screenshots of the iPad Pro (3rd gen) 12.9" must contain either the
+string `iPad Pro (12.9-inch) (3rd generation)`, `IPAD_PRO_3GEN_129`, or `ipadPro129`
+(App Store Connect's internal naming of the display family for the 3rd generation iPad Pro)
+in its filename to be assigned the correct display family and to be uploaded to
+the correct screenshot slot in your app's metadata.
+
+### Other Platforms
+
+#### Apple TV
+
+Apple TV screenshots should be stored in a subdirectory named `appleTV` with language
+folders inside of it.
+
+#### iMessage
+
+iMessage screenshots, like the Apple TV ones, should also be stored in a subdirectory
+named `iMessage`, with language folders inside of it.