Challenge setup + creation docs

[burturt]

We need some sort of docs to make onboarding for both devs and challenge writers easier and more streamlined beyond the 50 page readme.md that's there right now. Some docs are available at ACM Drive > 2022-23 > Cyber > Reference Docs > Cyber Instancer

[bliutech]

Should we set up a doc/ and use mdbook. We are open sourcing this so it would be nice to have this here. We might then need to debate whether to link the docs here or the actual instancer URL. We could also create a supporting repo just for docs as well.

[bliutech]

Or actually, perhaps a GitHub Wiki is the simplest solution.