Show some sort of version in the interactive tutorial.

I was talking to @tomglenn and we agree tha It's hard to know when Pathfinder's loaded a newly pushed to GitHub version of an interactive tutorial, and it's hard for users to report bugs against a specific version of a tutorial as there's no version displayed in Pathfinder.

Suggest that we use the GitHub commit hash for the `unstyled.html` file as the version identifier and have some sort of template markup in the `unstyled.html` file... this could then be populated by a GitHub action or something?