Tweak release docs

RELEASE.md

@@ -156,15 +156,8 @@ Tagged Docker images will be pushed to Dockerhub.
 
     docker run -ti dolfinx/dolfinx:v0.5.0
 
-Do *not* update the `stable` tag using `docker pull` and `docker push`. Instead,
-install the `regclient` utility https://github.com/regclient/regclient using the
-provided binaries. `regclient` can properly handle copying multi-architecture images.
-
-    regctl registry login docker.io
-    regctl image copy dolfinx/dolfinx:<tag> dolfinx/dolfinx:stable 
-    regctl image copy dolfinx/lab:<tag> dolfinx/lab:stable 
-    regctl image copy dolfinx/dev-env:<tag> dolfinx/dev-env:stable 
-    regctl image copy dolfinx/dolfinx-onbuild:<tag> dolfinx/dolfinx-onbuild:stable
+Use the Update stable Docker tag workflow to update/link `:stable` to e.g.
+`v0.5.0`.
 
 ### pypa