folders demo

This is a demo of the new folder-as-page behavior. Any directory under a content section can hold its own notes, and the directory itself becomes a clickable row in the parent's table.

A folder's row shows the tags from its info.md (so this folder displays demo and folder-test). Click into the folder and you'll see this description above the children table.

Folders can nest arbitrarily — there's a Recursive examples subfolder inside this one that goes one level deeper to show that off.