Where Should We Mention `--generator` Escaping?

[InsertCreativityHere]

I don't think it's worth mentioning in the help message.
And now that the parsing is tolerant, users will rarely be informed about escaping via CLI error messages.

But. We don't really have anywhere else talking about the slicec command-line.

[externl]

Maybe just put in the slicec README.md in this repo?