Docs improvement for projects with R via the VSCode extension

[hfrick]

Trying to deploy a quarto report with R code, I went from the docs landing page to the VS Code Extension page and added the renv lock file. Things were not working, so I went to the Troubleshooting page which also only mentions renv. Only when I poked around the configuration page did I notice the [r] section in the config toml and added that (even though the R version, etc, is in the renv lock file).

Mentioning the [r] section along with the renv lock file requirement in the guide to using the extension would have helped me navigate this more quickly.