I reported this issue in the docs repo, interestingly when I tried to submit a PR to fix it, I noticed it was updated to:
(set-env!
:source-paths #{"content"}
:dependencies '[[perun "0.4.2-SNAPSHOT" :scope "test"]])
(require '[io.perun :as perun])
and run boot perrun/markdown
https://github.com/hashobject/perun.io/blob/master/resources/guides/getting-started.md
So a fix may not have been published yet.1👍