[Retr0id]

I suspect even a majority of HN users visited the page on a mobile device, and were not in a position to immediately follow the instructions.

[Novosell]

Android allows you to create directories.

[Retr0id]

As does iOS, but the instructions given were for a desktop device.

[prmoustache]

So what? It is mentionned in the introduction that it is meant for computer users:

"What do I need?

You need a computer with internet access. I wrote this book in a generic way so that it would be applicable for people using macOS, Windows, or Linux. If I point you toward software to install, it will be free (or have a usable free tier) and will be cross-platform (or I will offer platform alternatives)." https://htmlforpeople.com/intro/#what-do-i-need%3F

[IshKebab]

So? How many people are editing HTML on their phones?