Patterns: reduce annoyance for writers of having a flat folder?

[Eric-Arellano]

Having all the guides in a single flat "guides" folder makes it more annoying for writers to work with: #1294.

Note that the URLs should be flat, like guides/my-file, not guides/my-folder/my-file. But it's annoying to be flat with the docs behind-the-scenes.

Fixing this would require some new mechanisms from the docs app to have files not colocated with the _toc.json. It's unclear how complex this would be.