message: chore(readme): add dev section
diff: @@ -19,6 +19,8 @@ React Flow is a library for building node-based graphs. You can easily implement
  - [Minimap](#minimap)
  - [Controls](#controls)
  - [Examples](#examples)
  +- [Development](#development)
  +- [Testing](#testing)
  # Key Features
  @@ -244,6 +246,24 @@ You can find all examples in the [example](example) folder or check out the live
  - [inactive](https://react-flow.netlify.app/inactive)
  - [custom node](https://react-flow.netlify.app/custom-node)
  +## Development
  +
  +If you want to contribute or develop some custom features the easiest way is to start the dev server:
  +
  +```
  +npm run dev
  +```
  +
  +This serves the content of the `examples` folder and watches changes inside the `src` folder. The examples are using the source of the `src` folder.
  +
  +## Testing
  +
  +Testing is done with cypress. You can find all test in the [`integration/flow`](/cypress/integration/flow) folder. In order to run the test you can do:
  +
  +```
  +npm run test
  +```
  +
  ## Thanks!
  