Fix `checkRd` notes

[milanmlft]

R CMD check is showing a bunch of warnings that look like this:

N  checking Rd files ...
   checkRd: (-1) build_episode_md.Rd:32: Lost braces; missing escapes or markup?
       32 | {knitr} output.}
          | 

See for example https://github.com/carpentries/sandpaper/actions/runs/10153800168/job/28077829634#step:12:304 This should fix that.

I also updated some outdated docs, by running devtools::document()

[ErinBecker]

Thanks @milanmlft! This looks great. The checks are failing due to a problem that @froggleston has fixed with https://github.com/carpentries/sandpaper/pull/600, which has now been merged. Could you please pull down the changes to main into your fork, which will retrigger the tests? They should pass and then we can merge this.