Add comment to locking code

pkg/state/state.go

@@ -360,7 +360,9 @@ func (s *State) Init(ctx context.Context) error {
 	}
 	defer tx.Rollback()
 
-	// Try to obtain an advisory lock
+	// Try to obtain an advisory lock.
+	// The key is an arbitrary number, used to distinguish the lock from other locks.
+	// The lock is automatically released when the transaction is committed or rolled back.
 	const key int64 = 0x2c03057fb9525b
 	_, err = tx.ExecContext(ctx, "SELECT pg_advisory_xact_lock($1)", key)
 	if err != nil {