Add note on how to build optimized benchmark executables.

benchmark/README.md

@@ -8,4 +8,11 @@ This package provides micro-benchmarking & profiling tools for:
 These are mostly used to compare effects of changes during development and should be taken with a grain of salt.
 
 Also see the full-application benchmark in https://github.com/objectbox/objectbox-dart-performance 
-which provides a better picture of the potential "real world" performance. 
+which provides a better picture of the potential "real world" performance.
+
+## Compile for production
+To get the most optimized version, build executables instead of running on Dart VM, for example:
+
+`dart compile exe bin/basics.dart`
+
+See https://dart.dev/tools/dart-compile for more options.