Demo: note why closure is not used for run async (#19)

Author: greenrobot-team

objectbox/example/flutter/objectbox_demo/lib/objectbox.dart

@@ -56,6 +56,9 @@ class ObjectBox {
   Future<void> addNote(String text) =>
       store.runInTransactionAsync(TxMode.write, _addNoteInTx, text);
 
+  /// Note: due to [dart-lang/sdk#36983](https://github.com/dart-lang/sdk/issues/36983)
+  /// not using a closure as it may capture more objects than expected.
+  /// These might not be send-able to an isolate. See Store.runAsync for details.
   static void _addNoteInTx(Store store, String text) {
     // Perform ObjectBox operations that take longer than a few milliseconds
     // here. To keep it simple, this example just puts a single object.

objectbox/example/flutter/objectbox_demo_sync/lib/objectbox.dart

@@ -53,6 +53,9 @@ class ObjectBox {
   Future<void> addNote(String text) =>
       store.runInTransactionAsync(TxMode.write, _addNoteInTx, text);
 
+  /// Note: due to [dart-lang/sdk#36983](https://github.com/dart-lang/sdk/issues/36983)
+  /// not using a closure as it may capture more objects than expected.
+  /// These might not be send-able to an isolate. See Store.runAsync for details.
   static void _addNoteInTx(Store store, String text) {
     // Perform ObjectBox operations that take longer than a few milliseconds
     // here. To keep it simple, this example just puts a single object.