Ah hah...

So the link on developer.puri.sm seems to be outdated, it points to the web app which is not what we need. There is a section for downloading the RIOT native app if you Google the app outside of Purism searches.

Here it is: RIOT app.

Registration was fairly straight forward at that point. Once you have a matrix account you can use the room directory page inside the app to paste in the talk.puri.sm and then search for the "librem-5" or any of the other Purism rooms.

The feedback loop for this blog is also coming together, so good progress.