* guix-jupyter-container.scm (kernel-info->html): Add warning at
  envrionment creation.
  (reply-execute-request): Update list ref.
* guix-jupyter-kernel.scm: Update list ref.
* guix-kernel/magic.scm (magic-env?): Test separator.
* tests/magic.scm (magic-no-code): Update string.
* README.org (How to use it): Update 'environment'.
* guix-kernel-demo.ipynb: Update with new syntax.