Write a main README.md that comply with the milestone criteria

Issue

The project does not hold a README.md.

Criteria

• The scientific context is clearly explained in the README.md
• The project objectives are clearly explained in the README.md
• Instructions on how to proceed are detailed in the README.md
• There is a description of the input data
• There are instructions on how to retrieve the input data (doi or URL, additional scripts can be provided)