Feature request: action description

Today, `workshop actions` will print a list of actions with the related *code* definition. This can be cryptic. It would be very nice if we could somehow add some `help` messages to it, so that we can describe:
- what it does
- what are the expected parameters

That is, in general, allowing the user understand what the point of an action is and how to use it.

Start by locating the implementation of `workshop actions` and how it renders related action code definitions. Inspect existing action declarations and any CLI tests, then determine how help text and expected parameters should be represented and displayed; done means the listing explains what each action does and how to use it.

Written by the indexing model from the issue text.