Initial WiFi Configuration

I’ve tried looking through the docs, but everything I’ve found either doesn’t work for me or has broken links (did the site layout fundamentally change or something? Seems like there are tons of broken links.)
If this has already been answered I’m happy to follow a link to the solution though, and I apologize for the noise.

Anyway, I got HassOS 4.13 running with a wired ethernet connection on a Raspberry Pi 3, and I can log in as root. From there I’m not so sure how I can set up my wifi: can I do it from the CLI? Is there a way of doing this in the HomeAssistant UI?

I’ve seen that people typically set this up by either mounting the SD card or using a USB stick. I’m on a Mac, and that seems to be giving me difficulty with modifying the SD card… Disk Utility doesn’t seem to let me edit it, and I tried mounting the SD card from shell (using the mount command) but the changes didn’t seem to persist (when I logged into the Raspberry Pi as root, then ran login, then ran ls /CONFIG/network there was nothing there).

AFAICT my best bet would be to just edit the file from the Raspberry Pi directly, but the file system seems to be read-only even when I’m logged in as “root”. Is there a way to get to a regular shell and just edit the file? That would make my life a whole lot easier.

Wired is really the way to go for any server application, but if you want to use WiFi, here’s a guide: Guide: Connecting Pi with Home Assistant OS to wifi (or other networking changes)