List packages needed to use Cloudsmith script

The problem was reported on our mailing list.

There is no list of system dependencies needed to use the Cloudsmith script to install Stork packages.

Required dependencies:

• curl
• bash
• sed

We should also analyze the possibility of minimizing the required packages (at least we should try to eliminate bash as it is pretty big and unsuitable for some deployments, e.g.: Alpine Docker container).