Extend the documentation with a short troubleshooting section

[eggia3]

Add a small section to the README explaining common beginner mistakes (e.g. forgetting to fork the repository, not creating a new branch, or merge conflicts) and how to fix them. This would help new contributors avoid typical errors and improve the learning experience.

DoR:
The task is considered ready to be worked on once the target repository is known and the part of the documentation to be extended is clearly defined. The goal and scope of the change are understood, the effort is small and manageable, and there are no technical or organizational dependencies blocking the implementation.

DoD:
The task is considered done when the documentation has been successfully extended and the added text is clear, correct, and consistent with the existing formatting. The change has been reviewed and submitted as a commit or pull request to the repository.