Adds Decision Criteria to the probnet dict.

        Parameters
        ----------
        criterion: <Element Criterion at Decision Criteria Node in XML>
            etree Element consisting DecisionCritera tag.

        Examples
        -------
        >>> reader = ProbModelXMLReader()
        >>> reader.add_criterion(criterion)

def add_criterion(self, criterion):
        """
        Adds Decision Criteria to the probnet dict.

        Parameters
        ----------
        criterion: <Element Criterion at Decision Criteria Node in XML>
            etree Element consisting DecisionCritera tag.

        Examples
        -------
        >>> reader = ProbModelXMLReader()
        >>> reader.add_criterion(criterion)
        """
        criterion_name = criterion.attrib['name']
        self.probnet['DecisionCriteria'][criterion_name] = {}
        if criterion.find('AdditionalProperties/Property') is not None:
            for prop in criterion.findall('AdditionalProperties/Property'):
                prop_name = prop.attrib['name']
                prop_value = prop.attrib['value']
                self.probnet['DecisionCriteria'][criterion_name]['AdditionalProperties'][prop_name] = prop_value