fill in missing '$ ' in prompt

We should be consistent with the code blocks that are meant to be executed in the shell.

Personally, I don't like having `$ ` before commands. I think it is less readable, confusing (is `$` a command?), and makes copy-paste more difficult. I would sooner remove it everywhere, but we should at least be consistent.

Any thoughts about removing `$ ` everywhere? Or is it more conventional than I think? This would apply to the workshop-template as well.