Add a capability list.

        Adds either a CapabiltyList object specified in capability_list
        or else creates a Resource with the URI given in capability_list
        and adds that to the Source Description

def add_capability_list(self, capability_list=None):
        """Add a capability list.

        Adds either a CapabiltyList object specified in capability_list
        or else creates a Resource with the URI given in capability_list
        and adds that to the Source Description
        """
        if (hasattr(capability_list, 'uri')):
            r = Resource(uri=capability_list.uri,
                         capability=capability_list.capability_name)
            if (capability_list.describedby is not None):
                r.link_set(rel='describedby', href=capability_list.describedby)
        else:
            r = Resource(uri=capability_list,
                         capability='capabilitylist')
        self.add(r)