Update admin.md

doc/admin.md

@@ -164,24 +164,41 @@ support nulls or multi-attribute requests if they are encountered.
 It configures the periodic collection of statistics. Use `interval` in milliseconds to set the time between stats
 writings.
 
-By default, stats are logged to the standard log at level `INFO`. If the `persistence` flag is defined and set to
-`true`, stats are also stored in a collection named `kpis` in the mongo backend.
+```javascript
+stats: {
+    interval: 100;
+}
+```
+
+By default, stats are logged to the standard log at level `INFO`. You can also have your stats written
+to a collection named `kpis` in the mongo backend, if you do these two things:
+
+- Set the `stats.persistence` flag to `true`.
 
 ```javascript
 stats: {
     interval: 100;
-    persistence: false;
+    persistence: true;
 }
 ```
 
+- Schedule periodic collection of stats to mongo by calling `statsRegistry.addTimerAction`.
+
+```js
+statsRegistry.addTimerAction(statsRegistry.mongodbPersistence, function callback() {
+  // ... called after timer is enabled ...
+});
+```
+
 Each document in the `kpis` collection will have a `timestamp` attribute with the stat collection time, and an
 additional attribute for each of the stats created by calling the `statsRegistry.add` function, e.g.:
 
 ```json
 {
   "timeinstant": new ISODate("2024-07-29T00:00:00.000Z"),
   "deviceCreationRequests": 1334,
-  "deviceRemovalRequests": 454
+  "deviceRemovalRequests": 454,
+  "measureRequests": 4432
 }
 ```