metricbeat: Improve README, add notes about config

extensions/metricbeat/README.md

@@ -6,15 +6,31 @@ and ships them to the output that you specify, such as Elasticsearch or Logstash
 
 ## Usage
 
-If you want to include the Metricbeat extension, run Docker Compose from the root of the repository with an additional
-command line argument referencing the `metricbeat-compose.yml` file:
+To include Metricbeat in the stack, run Docker Compose from the root of the repository with an additional command line
+argument referencing the `metricbeat-compose.yml` file:
 
-```bash
+```console
 $ docker-compose -f docker-compose.yml -f extensions/metricbeat/metricbeat-compose.yml up
 ```
 
-## Documentation
+## Configuring Metricbeat
 
-[Official Docs](https://www.elastic.co/guide/en/beats/metricbeat/current/metricbeat-overview.html)
-[Running on Docker](https://www.elastic.co/guide/en/beats/metricbeat/current/running-on-docker.html)
-[Configuration reference](https://www.elastic.co/guide/en/beats/metricbeat/master/metricbeat-reference-yml.html)
+The Metricbeat configuration is stored in [`config/metricbeat.yml`](./config/metricbeat.yml). You can modify this file
+with the help of the [Configuration reference][metricbeat-config].
+
+Any change to the Metricbeat configuration requires a restart of the Metricbeat container:
+
+```console
+$ docker-compose -f docker-compose.yml -f extensions/metricbeat/metricbeat-compose.yml restart metricbeat
+```
+
+Please refer to the following documentation page for more details about how to configure Metricbeat inside a
+Docker container: [Run Metricbeat on Docker][metricbeat-docker].
+
+## See also
+
+[Metricbeat documentation][metricbeat-doc]
+
+[metricbeat-config]: https://www.elastic.co/guide/en/beats/metricbeat/master/metricbeat-reference-yml.html
+[metricbeat-docker]: https://www.elastic.co/guide/en/beats/metricbeat/current/running-on-docker.html
+[metricbeat-doc]: https://www.elastic.co/guide/en/beats/metricbeat/current/index.html