Simplify references to sets (#1042)

docs/learn/fundamentals/stellar-consensus-protocol.mdx

@@ -67,15 +67,17 @@ To transition between the states above, federated voting has the following rules
 
 - Confirm A if every node in a quorum slice accepted A
 
+## Consensus rounds
+
 Each consensus round is separated into two stages:
 
-**Nomination protocol**
+### Nomination protocol
 
 In the nomination protocol, candidate transaction sets are selected to be included in a ledger. Once a node confirms its first candidate, it stops voting to nominate any new transaction sets. It may still accept or confirm previously nominated statements. This guarantees that at some point, all nodes will converge on a candidate set. If every node on the network stops introducing new values but continues to confirm what other nodes confirmed, eventually, everyone will end up with the same list of candidates.
 
 A node may start the ballot protocol as soon as it confirms a candidate. After it confirms its first candidate and starts the ballot protocol, nomination continues running in the background.
 
-**Ballot protocol**
+### Ballot protocol
 
 The ballot protocol ensures that the network can unanimously confirm and apply nominated transaction sets. It consists of two steps: