26.3.2 Deriving Error enums

[njr0]

I think a little but more explanation would be helpful here.

I don't think the course has mentioned positional arguments to format strings before, and though I think people will guess that's what "{0}" is, it's not immedately apparent, looking at the code, that there's a argument for it to format.

Similarly, I think a few words about #[error and #[from might be useful.

[mgeisler]

Hey @njr0, yeah, we should expand the speaker notes on the page!

In general, I would like to see speaker notes on every page (#1083).

[mgeisler]

I created #1285 for this so it becomes more visible. In general, feel free to file issues for concrete problems like this 🙂