README: Add benchmarks.

Author: greenrobot-team

.github/benchmarks.png

@@ -30,9 +30,6 @@ If you'd like to contribute to the package as a developer, hack around, or just
 clone/check out this repository and run `./tool/init.sh` to regenerate code and get you started. Make sure to have a
 look at the [contribution guidelines](CONTRIBUTING.md) - all contributions are very welcome.
 
-## Benchmarks
-
-
 ## Packages
 
 This repository holds all ObjectBox Dart/Flutter packages as separate directories:

README.md

@@ -130,6 +130,15 @@ dev_dependencies:
 
 Continue with the [examples README](example/README.md) to learn how to create entities and use the ObjectBox API.
 
+## Benchmarks
+
+We tested CRUD operations (create, read, update, delete). Each test was run multiple times and executed 
+manually outside of the measured time. Data preparation and evaluation were also done outside of the measured time.
+
+![](https://raw.githubusercontent.com/objectbox/objectbox-dart/main/.github/benchmarks.png)
+
+You can run these yourself using our [objectbox-dart-performance](https://github.com/objectbox/objectbox-dart-performance) Flutter benchmark app.
+
 ## Help wanted
 
 ObjectBox Dart is open to contributions and feedback on [GitHub](https://github.com/objectbox/objectbox-dart/issues).