Until there is such a link you can bookmark and follow
https://discourse.mcneel.com/tag/service-release
https://discourse.mcneel.com/tag/release-candidate
For Rhino 7 service releases at this moment the latest post in its thread is Rhino 7 Service Release Available - #19 by brian
For Rhino 7 service release candidates at this moment the latest post in its thread is Rhino 7 Service Release Candidate Available - #52 by brian
Logged request as RH-67031 Access to changelog from update notification