Update README with new instructions on how to configure the plugin.

plugins/newrelic/README.md

@@ -7,16 +7,38 @@ Website: [https://newrelic.com](https://newrelic.com)
 
 ## Getting Started
 
-Add New Relic REST API Key to `app-config.yaml`
+This plugin uses the Backstage proxy to securely communicate with New Relic's
+APIs. Add the following to your `app-config.yaml` to enable this configuration:
 
 ```yaml
-newrelic:
-  api:
-    baseUrl: 'https://api.newrelic.com/v2'
-    key: <NEW_RELIC_REST_API_KEY>
+proxy:
+  '/newrelic/apm/api':
+    target: https://api.newrelic.com/v2
+    headers:
+      X-Api-Key:
+        $env: NEW_RELIC_REST_API_KEY
 ```
 
-New Relic Plugin Path: [/newrelic](http://localhost:3000/newrelic)
+In your production deployment of Backstage, you would also need to ensure that
+you've set the `NEW_RELIC_REST_API_KEY` environment variable before starting
+the backend.
+
+While working locally, you may wish to hard-code your API key in your
+`app-config.local.yaml` like this:
+
+```yaml
+# app-config.local.yaml
+proxy:
+  'newrelic/apm/api':
+    headers:
+      X-Api-Key: NRRA-YourActualApiKey
+```
+
+Read more about how to find or generate this key in
+[New Relic's Documentation](https://docs.newrelic.com/docs/apis/get-started/intro-apis/types-new-relic-api-keys#rest-api-key).
+
+See if it's working by visiting the New Relic Plugin Path:
+[/newrelic](http://localhost:3000/newrelic)
 
 ## Features