Augment the README with a mention of the new GH action based release tooling as an alternative to this script

[fingolfin]

E.g. the aclib package uses this workflow; all one has to do is to copy https://github.com/gap-packages/aclib/blob/master/.github/workflows/release.yml

See also https://github.com/gap-actions/release-pkg and https://github.com/gap-actions/update-gh-pages/.