Update README.md

[dmikusa]

Change references from gcr.io to docker.io for stack/builders.

[andrejusc]

@dmikusa - I think instead of this in your change:
run-image = "docker.io/paketo-buildpacks/run:tiny-cnb"
it should be this (and could be for other involved images as well):
run-image = "docker.io/paketobuildpacks/run:tiny-cnb"

i.e. from DockerHub without extra dash in the image name.

At least I have such:

podman image ls
REPOSITORY                          TAG         IMAGE ID      CREATED       SIZE
docker.io/paketobuildpacks/run      tiny-cnb    63216a76b12e  4 days ago    19.2 MB
docker.io/paketobuildpacks/builder  tiny        5320ff45280d  43 years ago  633 MB
docker.io/paketocommunity/rust      latest      dfa09c5bb7cd  43 years ago  30.9 MB

Could you double-check?

[dmikusa]

Shoot. You're right @andrejusc Docker Hub annoyingly doesn't allow a - in the org/user name. I'll fix that.