Document new majority-wins voting strategy

While the default voting strategy is still a primary-wins one, the
voting strategy used for strong consistency has been changed from
requiring all nodes to agree to only requiring primary and half of the
secondary nodes to agree.

Adapt the documentation to mention this change to the voting strategy.

doc/administration/gitaly/praefect.md

@@ -991,8 +991,12 @@ information, see the [strong consistency epic](https://gitlab.com/groups/gitlab-
 
 To enable strong consistency:
 
-- In GitLab 13.3 and later, reference transactions are enabled by default with
-  a primary-wins strategy. This strategy causes all transactions to succeed for
+- In GitLab 13.4 and later, the strong consistency voting strategy has been
+  improved. Instead of requiring all nodes to agree, only the primary and half
+  of the secondaries need to agree. To enable this strategy, disable the
+  `:gitaly_reference_transactions_primary_wins` feature flag.
+- In GitLab 13.3, reference transactions are enabled by default with a
+  primary-wins strategy. This strategy causes all transactions to succeed for
   the primary and thus does not ensure strong consistency. To enable strong
   consistency, disable the `:gitaly_reference_transactions_primary_wins`
   feature flag.