contributing.md refers to a develop branch that does not exist

[madbkr]

Description of the issue

The contributing.md file asks to branch from the develop branch. This branch does not seem to exist anymore.

Ideas of solution

Either change the contributing file or get this branch back in use.

Context and Environment

• Version used:
• Operating system:
• Environment setup and (python) version:

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md