docs: update CONTRIBUTING

Signed-off-by: Thomas Schuetz <thomas.schuetz@t-sc.eu>

CONTRIBUTING.md

@@ -27,6 +27,7 @@ We're happy that you want to contribute to this project. Please read the section
 **How do I contribute?**
 - Fork the repository and clone it locally
 - Create a new branch and follow [conventional commits](https://www.conventionalcommits.org/en/v1.0.0/) guidelines for work undertaken
+- Assign yourself to the issue, if you are working on it (if you are not a member of the organization, please leave a comment on the issue)
 - Make your changes
 - Keep pull requests small and focused, if you have multiple changes, please open multiple PRs
 - Create a pull request back to the upstream repository and follow follow the [pull request template](.github/pull_request_template.md) guidelines.