* Added note about Docker credentials store
Docker might use a credentials store when logging in to docker repositories, see https://docs.docker.com/engine/reference/commandline/login/#credentials-store. In that case you don't find the `auth` token in the `config.json` file. I added a note that this might happen, in order to prevent confusion.
* added "NOTE:" to the Docker credentials store note
as suggested in PR review
88212bdfa9