Ah no wonder I couldn’t find it - those changes are all gone now - the README files just point to the specifications site index pages.
NB: the link change is actually correct, as the Architecture Overview went to the BASE component a long time ago. Github is doing something funny with the URLs.
See various pull requests by Jan Mewes in specifications-RM Git repo. https://github.com/openEHR/specifications-RM/pulls?q=is%3Apr+is%3Aclosed