docs: explain how to add metrics to grafana (#11875)

etc/README.md

@@ -2,7 +2,8 @@
 
 This directory contains miscellaneous files, such as example Grafana dashboards and Prometheus configuration.
 
-The files in this directory may undergo a lot of changes while reth is unstable, so do not expect them to necessarily be up to date.
+The files in this directory may undergo a lot of changes while reth is unstable, so do not expect them to necessarily be
+up to date.
 
 ### Overview
 
@@ -11,8 +12,78 @@ The files in this directory may undergo a lot of changes while reth is unstable,
 
 ### Docker Compose
 
-To run Reth, Grafana or Prometheus with Docker Compose, refer to the [docker docs](/book/installation/docker.md#using-docker-compose).
+To run Reth, Grafana or Prometheus with Docker Compose, refer to
+the [docker docs](/book/installation/docker.md#using-docker-compose).
 
-### Import Grafana dashboards
+### Grafana
 
-Running Grafana in Docker makes it possible to import existing dashboards, refer to [docs on how to run only Grafana in Docker](/book/installation/docker.md#using-docker-compose#run-only-grafana-in-docker).
+#### Adding a new metric to Grafana
+
+To set up a new metric in Reth and its Grafana dashboard:
+
+1. Add the metric to the codebase following the [metrics section](../docs/design/metrics.md#creating-metrics)
+   documentation.
+
+2. Build the Reth image:
+
+    ```bash
+    docker build . -t reth:local
+    ```
+
+   Modify the [docker-compose](./docker-compose.yml) file to use your locally built image for the Reth service.
+
+3. Run Docker Compose:
+
+    ```bash
+    docker compose -f etc/docker-compose.yml -f etc/lighthouse.yml up -d
+    ```
+
+4. Access Grafana:
+
+    - Open `http://localhost:3000/` in a browser
+    - Log in with username and password `admin`
+    - Navigate to the `Dashboards` tab
+
+5. Create or modify a dashboard:
+
+    - Select an existing dashboard or create a new one
+    - Click `Add` > `Visualization` to create a new panel
+
+6. Configure your metric panel:
+
+    - Set a panel title and description
+    - Select metric(s) from the `Metrics browser` or use the `PromQL` terminal
+    - Document your metric(s) by setting units, legends, etc.
+    - When adding multiple metrics, use field overwrites if needed
+
+7. Save and arrange:
+
+    - Click `Apply` to save the panel
+    - Drag the panel to desired position on the dashboard
+
+8. Export the dashboard:
+
+    - Click `Share` > `Export`
+    - Toggle `Export for sharing externally`
+    - Click `Save to file`
+
+9. Update dashboard file:
+    - Replace the content of the corresponding file in the [dashboards folder](./grafana/dashboards) with the exported
+      JSON
+
+Your new metric is now integrated into the Reth Grafana dashboard.
+
+#### Import Grafana dashboards
+
+In order to import new Grafana dashboards or update a dashboard:
+
+1. Go to `Home` > `Dashboards`
+
+2. Click `New` > `Import`
+
+3. Drag the JSON dashboard file to import it
+
+4. If updating an existing dashboard, you will need to change the name and UID of the imported dashboard in order to
+   avoid conflict
+
+5. Delete the old dashboard