added a comment

fdbserver/ClusterController.actor.cpp

@@ -1259,6 +1259,9 @@ public:
 	}
 
 	// FIXME: determine when to fail the cluster controller when a primaryDC has not been set
+
+	// This function returns true when the cluster controller determines it is worth forcing
+	// a master recovery in order to change the recruited processes in the transaction subsystem.
 	bool betterMasterExists() {
 		const ServerDBInfo dbi = db.serverInfo->get();