tutorial on citation in R Markdown needs clarification

When searching for information on citations on the internet, I arrived at the tutorial on citation in R Markdown by @hansvancalster and @florisvdh (which is nice, I think).

However, when using this tutorial, I immediately got in troubles: it is recommended (or even needed) to enter VME mode, but the button that is shown in the pictures, is not present in my RStudio, despite I have the newest typical INBO installation of R & RStudio (new version since last friday). I moreover have markdown, rmarkdown and bookdown installed. So I suppose for this VME mode, an additional installation should be done? It would be helpful if the tutorial would mention this.