Populate "Download Lesson Handout"

[jdrnevich]

I tried to have sandpaper automatically create a "Download Lesson Handout" following @lgatto attempt in bioc-intro by adding options(sandpaper.handout = TRUE) to the sandpaper-main.yaml. However, this didn't seem to do anything. Googling led me to here, which says you also need to add purl = TRUE to all code chunks you want to include. I tried doing this for episode 3, but it also didn't seem to do anything when I built locally using sandpaper::serve(). However, later after pushing all commits to this GitHub repo, merging the pull request and running the GitHub action, it did appear on the Episode sidebar of the github.io website.

• Add purl=TRUE to all/almost add R code chunks
• Check the resulting Lesson Handout for clarity/modifications needed