Add chapter on project structure

[lnnrtwttkhn]

• [ ] https://heidiseibold.ck.page/posts/setting-up-a-fair-and-reproducible-project
• [ ] https://github.com/bluegreen-labs/R_project_template
• [ ] https://onlinelibrary.wiley.com/doi/10.1002/ece3.9961
• [ ] https://inbo.github.io/checklist/