Documentation: Clarify how to use prometheus locally (#72846)

Co-authored-by: Fiona Artiaga <89225282+GrafanaWriter@users.noreply.github.com>

contribute/backend/instrumentation.md

@@ -140,13 +140,15 @@ If you want to guarantee the existence of metrics before any observations has ha
 
 ### How to collect and visualize metrics locally
 
+1. Ensure you have Docker installed and running on your machine
 1. Start Prometheus
 
    ```bash
    make devenv sources=prometheus
    ```
 
-2. Use Grafana Explore or dashboards to query any exported Grafana metrics
+1. Run Grafana, and create a Prometheus datasource if you do not have one yet. Set the server URL to `http://localhost:9090`, enable basic auth, and type in the same auth you have for local Grafana
+1. Use Grafana Explore or dashboards to query any exported Grafana metrics. You can also view them at http://localhost:3000/metrics
 
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