Asciidoc is wonderful, especially with Asciidoctor, which has now become the de-facto standard renderer. (It's what github uses, for example.) It's as easy as

Asciidoc is wonderful, especially with Asciidoctor, which has now become the de-facto standard renderer. (It's what github uses, for example.) It's as easy as Markdown (and the syntax is so similar it's not hard to switch), but just has much better design, along with supporting the features you need once you start having enough documentation that you need an actual tech writer. Plus, it's still just plain text, so it plays nice with Git and is thoroughly readable without being rendered.