Update developer.md

docs/developer.md

@@ -26,6 +26,8 @@ Alternatively (e.g. if your system is not supported by the setup.sh script), fol
 
 This will install all required tools for development, including `pytest`, `flake8`, `mypy`, and `coveralls`.
 
+Then install the git hook scripts by running `pre-commit install`
+
 Before opening a pull request, please familiarize yourself with our [Contributing Guidelines](https://github.com/freqtrade/freqtrade/blob/develop/CONTRIBUTING.md).
 
 ### Devcontainer setup