added README for Xcode asset project

util/ios_asset_project/README.md

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+# Icons, Launch Storyboards and the Assets Catalog
+
+Our friends from _distriqt_ have written [extensive documentation][1] on how to add an icon (in numerous variants), as well as a launch screen, for deployment to iOS.
+This folder contains an Xcode project that you can use to customize and export the required files.
+
+* After making the modifications (as described in the above link), build the project with Xcode.
+* Then, right-click on "iOS Asset Project.app" (in the project navigator on the left) and select 'Show in Finder'.
+* In the Finder, click on the app file again and choose 'Show Package Contents'.
+* Copy the files `Assets.car` and `LaunchScreen.storyboardc` (optional) to the Starling Scaffold (`system` subfolder) or your own AIR project.
+
+[1]: https://docs.airnativeextensions.com/docs/tutorials/ios-icons-assets-car
+
+### Launch Screen storyboard vs. Harman 'Free Tier'
+
+On the "Free Tier" of AIR, you're required to show a splash screen with the AIR logo.
+The AIR SDK handles this via its own "launch screen" storyboard.
+It will replace any custom one you've made (like the one in this Xcode project).
+
+However, if you supply an `Assets.car` file (and you will, because it contains the app icon), you need to provide the splash image assets, as well.
+They're found in the AIR SDK (`lib/aot/res` folder), but I've also included them in the Xcode project.
+
+So, in the free tier:
+
+* Make sure the `Assets.car` file contains the AIR splash images.
+* Don't bother to customize and export the launch screen storyboard, as will be ignored by AIR.
+
+If you're in a commercial tier:
+
+* You can remove `splash_landscape` and `splash_portrait` from `Assets.xcassets` (by deleting them from the Xcode project).
+* Customize the launch screen storyboard, e.g. with your own logo and colors.
+* Include `LaunchScreen.storyboardc` when you copy over your assets from the compiled app.