Added OS text to README. (#283)

Author: redbrogdon

veggieseasons/README.md

@@ -1,10 +1,13 @@
 # Veggie Seasons
 
-An app that shows which fruits and vegetables are currently in season. It
+An iOS app that shows which fruits and vegetables are currently in season. It
 showcases Flutter's Cupertino package.
 
 [Available now in the App Store!](https://itunes.apple.com/is/app/veggie-seasons/id1450855435)
 
+**NOTE:** While Flutter supports many platforms, this application is designed
+specifically for iOS. It's not intended to be run on Android, web, or desktop.
+
 ## Goals
 
 * Show how to build an interface that iOS users will feel right at home