[DOC] Improve guidelines for the review process

[acocac]

Describe the proposed improvement to the documentation

The notebook contribution #239 comes with some missing information for the author(s)/reviewers:

• The REVIEW PR in the notebook repository should be forked from the authors to implement updates.
• The reviewers should focus in the forked REVIEW to verify changes.
• Editors should be aware about above processes.

Additional information

This changes should be implemented in the guidelines for reviewers, authors and editors.