Missing R commands throughout chapter 4

[jgbaum]

First, thanks for putting this together. It's truly a great resource!

I wanted to report that I was working through Chapter 4 here (https://www.singlecellcourse.org/introduction-to-rbioconductor.html#data-types) and noticed that the R commands seem to be missing from the rendered output and all that is shown is the output of the R commands. For instance, in section 4.3 (Data types), I would expect to see something like:

var <- 10

However, all that is shown is:

There are similar issues with all of the code blocks in the document. I have tried several browsers to rule out browser-specific issues.

Looking at the code base in this repo, the content seems different than what is rendered on singlecellcourse.org, so I can't tell where the issue is coming from. Anyway, I thought you may want to address it as it would help users to run those commands and see the output.

Thank you!