Add explanation for default port

docs/sources/getting-started/get-started-grafana-prometheus.md

@@ -78,7 +78,7 @@ The following example shows you the code you should add. Notice that static conf
     ./prometheus --config.file=./prometheus.yml
    ```
 
-1. Confirm that Prometheus is running by navigating to `http://localhost:9090`.
+1. Confirm that Prometheus is running by navigating to `http://localhost:9090`. 9090 is the default port, but could change depending on their prometheus installation.
 
 You can see that the node_exporter metrics have been delivered to Prometheus. Next, the metrics will be sent to Grafana.