Add release workflow to README

[emirkmo]

When devel is ready, from @rhandberg:

1. Update the VERSION file with the new version-name (master-vX.Y.Z), push the change up.
2. Ensure the tests pass on GitHub.
3. Merge the devel branch into the master branch.
4. Create tag on new master branch (vX.Y.Z).
5. Merge the new master branch back into the devel branch. This ensures that the tag is in the history of the devel branch.
6. Once CI/CD tests pass on tagged master branch, go to GitHub releases to review new release.