Parameters
		----------
		pd.Series
		term -> frequency
		Returns
		-------
		PriorFactory

def use_custom_term_frequencies(self, custom_term_frequencies):
		'''
		Parameters
		----------
		pd.Series
		term -> frequency
		Returns
		-------
		PriorFactory
		'''
		self.priors += custom_term_frequencies.reindex(self.priors.index).fillna(0)
		return self