Allow Tim Berners Lee to abstain in Unanimous Short Circuit votes

This removes him from the being on critical path for the Council's
Unanimous Short Circuit votes, without affecting any other role he has
as a TAG and Council member.

See #874

index.bs

@@ -2453,6 +2453,8 @@ Unanimous Short Circuit</h5>
 	the Team recommends a resolution
 	and every potential member of a Council who is not renouncing their seat
 	votes affirmatively (no abstentions) to adopt this resolution.
+	As an exception, Tim Berners Lee <em class=rfc2119>may</em> abstain
+	without blocking the adoption of the resolution.
 
 	This step <em class=rfc2119>may</em> be run concurrently with [[#council-participation]]
 	and prior to choosing a [=W3C Council Chair|Chair=].