Wikilinks on wiki docs

To build a good markdown import/export roundtrip, it looks like the standard in 2022 is [[wikilinks]].
Right now I suspect we will get
[markdown links](some url that is not the title, like a big hash id). This destroys any usefulness for
import/export roundtrip.
Given how the new 'courses' functionality will use wiki docs heavily, and people building a CBC will rely heavily on these, it's time to build up the best wiki docs possible :)