Update flutter build apk -h to indicate that target arch is not supported in debug mode. (#154111)

Part of #153359

packages/flutter_tools/lib/src/commands/build_apk.dart

@@ -50,7 +50,9 @@ class BuildApkCommand extends BuildSubCommand {
       ..addMultiOption('target-platform',
         defaultsTo: <String>['android-arm', 'android-arm64', 'android-x64'],
         allowed: <String>['android-arm', 'android-arm64', 'android-x86', 'android-x64'],
-        help: 'The target platform for which the app is compiled.',
+        // https://github.com/flutter/flutter/issues/153359 tracks debug build type support.
+        help:
+            'The target platform for which the app is compiled. Supports release but not debug build types.',
       );
     usesTrackWidgetCreation(verboseHelp: verboseHelp);
   }