Like some other commenters, I disagreed with the headline. But the article says something more subtle than 'write documentation first'. Its points are:

* Write documentation alongside, ie as you go

* Use writing English (or your language) documentation as a way to clarify your thoughts: the process of writing is a tool to ensure something is well thought through

I disagreed with the headline because I interpreted it as writing end-user documentation, effectively a very detailed specification document, up-front and then writing code to match. In reality, coding is a process of discovery, and you need the flexibility to allow the implementation to change. Your goal might be known, but the path to that goal is flexible.

The article pitches writing that goal upfront. Visicalc had a few sample formulae. Nest had a press release written. But for both, and it's explicitly called out for Visicalc, the actual user-facing documentation was written alongside the code as the product developed. This solves the problem of not having documentation ready when the product is ready, too.

In short: misleading headline, insightful article. I'd like to take its suggestion of writing docs alongside implementation as implementation develops on board myself.