Don't double-count identical ballots from a single org in the Council

Adopting wording from #327 (comment)

index.bs

@@ -2389,6 +2389,11 @@ Council Participation, Dismissal, and Renunciation</h5>
 	the decision is made by simple majority,
 	with the [=Chair of the W3C Council=] breaking ties.
 
+	If the [=Council=] needs to resort to a vote,
+	and if two members of the council who share the same affiliation cast an identical ballot,
+	then their ballots count as a one vote,
+	not two.
+
 	If the [=W3C Council=] is unable to come to a conclusion within 90 days of being initially convened for a particular topic,
 	the [=Chair of the W3C Council=] <em class=rfc2119>must</em> inform the [=AC=] of this delay
 	and of the status of the discussions.