refactor(TripMonitorNotification): Add comment for comparator/sort fu…

…nction.

src/main/java/org/opentripplanner/middleware/models/TripMonitorNotification.java

@@ -24,6 +24,10 @@ public TripMonitorNotification(NotificationType type, String body) {
         this.body = body;
     }
 
+    /**
+     * Basic comparator that sets an arbitrary lower rank for initial reminders,
+     * so that they appear before other notifications after list sorting.
+     */
     public int sortOrder() {
         return type == NotificationType.INITIAL_REMINDER ? -100 : 0;
     }