In that folder is CHANGELOG.md[0] that indicates that this is unreleased. I'd say that including installation instructions for an unreleased version of the extension is exactly the issue that is being flagged.
You are going to want to reread the file you are quoting buddy. That changelog is indicative that the extension has been released. The Unreleased section seems to list features that are not yet included in the released version of the VS Code extension, and the future plans are features that have not been developed yet.
[0] https://github.com/blopker/codebook/blob/main/vscode-extensi...