def contribute_to_class(model_class, name='slots', descriptor=None):
    """
    Function that adds a description to a model Class.

    :param model_class: The model class the descriptor is to be added
    to.
    :param name: The attribute name the descriptor will be assigned to.
    :param descriptor: The descriptor instance to be used. If none is
    specified it will default to
    ``icekit.plugins.descriptors.PlaceholderDescriptor``.
    :return: True
    """
    rel_obj = descriptor or PlaceholderDescriptor()
    rel_obj.contribute_to_class(model_class, name)
    setattr(model_class, name, rel_obj)
    return True