Fix CloudSmith Alpine link in docs

We have here a wrong link to the CloudSmith script for Aline: https://dl.cloudsmith.io/public/isc/stork/cfg/setup/bash.apk.sh .

The correct one is: https://dl.cloudsmith.io/public/isc/stork/setup.alpine.sh .

See https://cloudsmith.io/~isc/repos/stork/setup/#formats-alpine