I log in as johndoe:
$ ./venv-py3.4/bin/pierone login --user johndoe
Getting OAuth2 token "pierone".. OK
Storing Docker client configuration in /home/jdoe/.docker/config.json.. OK
This has written some Docker configuration:
$ cat  ~/.docker/config.json | jq '.'
{
  "auths": {
    "https://pierone.repo": {
      "email": "no-mail-required@example.org",
      "auth": "b2F1dGgyOjQ4NTEyODZiLTZmZTctNTBlYy05MjAxLTlhNzkwNjM5NzQzMA=="
    },
    "null ...