Description

This PR contains the vignettes as tutorials, as described in #262
All vignettes can be found in the tutorials/content/tutorials folder.
One tutorial equals one vignette. The name of the file follows the convention vignette + package_name+ vignette_name.
The structure of the index.md uses the following structure:

---
title: "..."
description: "Vignette for the R package ...."
authors: ...
date: ...
categories: ["r"]
tags: ["r", "vignette", ...]
output: 
    md_document:
        preserve_yaml: true
        variant: markdown_github
---

See the vignette/tutorial at <link>

@florisvdh @peterdesmet @ThierryO the revision is all yours

Task list

• My tutorial or article is placed in a subfolder of tutorials/content
• The filename of my tutorial or article is index.md. In case of an Rmarkdown tutorial I have knitted my index.Rmd to index.md (both files are pushed to the repo).
• I have included tags in the YAML header (see the tags listed in the tutorials website side bar for tags that have been used before)
• I have added categories to the YAML header and my category tags are from the list of category tags

Previewing the pull request

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