I'd fix it myself, but I did a bit of digging and not exactly sure why it's not linking properly. I'm assuming someone else will be able to find it much more quickly :)
https://rust-embedded.github.io/embedonomicon/memory-layout.html, which is what shows up in hyperlinks in the Embedonomicon, ends up taking you to http://embedonomicon.rust-embedded.org/memory-layout.html.
Thanks for this resource - learned a lot from it.