container-toolbox: Don't try to copy a non-existent file
    
    There's no README.md to copy, and it polluted the build logs with a
    needless error message:
      INFO anaconda:program: cp: cannot stat '/README.md': No such file or
          directory
    
    The Container/Dockerfile equivalent of the fedora-toolbox OCI images
    have a /README.md because it used to be required by the Fedora Container
    Guidelines [1].  However, that's no longer the case [2] and neither the
    fedora nor the fedora-minimal base images have it.  Therefore, it's not
    worth bothering with it.
    
    [1] https://docs.fedoraproject.org/en-US/containers/
    
    [2] Fedora Container Docs commit 4fc6827a23ddc265
        https://github.com/containers/docs/commit/4fc6827a23ddc265
        https://github.com/containers/docs/pull/5
    
    Fallout from 48e2c3b5598de32f6dabfb5d1985d17aeab97d58
    
    https://pagure.io/fedora-kickstarts/pull-request/1028