How to create a sidebar navigation different from the content structure?

Given a desired navigation configuration:

	- section:

And the current content structure:


Initially, I created placeholder directories with placeholder files with manual links to real documents. But it slows down my site building dramatically.
How can I recreate the desired navigation structure via configs?

Configure your permalinks:

Menus for your own content can be build entirely in the front-matter of your content files. The resulting menu structure does not depend on the underlying folder structure.

The front-matter looks like this:

    name: Markdown
    parent: intro

It may feel a little weird in the beginning to have no centralized menu configuration, but its very convenient. The order of the menu entries follows the page weight, but you can also attach an extra weight to every menu entry.

Its documented here.