MkDocs was exactly what I was looking for. Out of the box it does precisely what I want it to.

Docsify, VuePress and Eleventy were also options I was looking at. I tried docsify first, it looked promising but it didn't auto-gen navigation for me.

After testing out MkDocs, I didn't see a reason to continue. I'll still try VuePress and Eleventy, as well as any other options that folks suggest.

Will leave this question unanswered in case someone comes along with a better option.