add readme

README.md

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 # netdata-action
-Use Netdata to record CI metrics
+
+> [!CAUTION]
+> This action is a work in progress.
+
+This action sets up [netdata](https://github.com/netdata/netdata) to send metrics to a [Prometheus server](https://github.com/prometheus/prometheus) via the [Prometheus remote write API](https://learn.netdata.cloud/docs/exporting-metrics/prometheus-remote-write) while GitHub Actions is running. This gives you detailed visibility into the performance of your GitHub Actions workflows, which can be helpful optimizing your workflow performance.
+
+![image](https://github.com/user-attachments/assets/14dd94f1-8c12-41ff-8ce2-f3e8d7d7a32f)
+
+In this example, the application server consumes only 2 CPUs out of 4. Further digging shows that our E2E test setup only runs 2 instance of the application server. We can increase the number of instances to 4 to better utilize the available resources and make tests run faster.
+
+Without any configuration, Netdata automatically tracks hundreds of metrics about your system's performance. Here are some metrics we find useful:
+
+<!-- prettier-ignore -->
+| Metric | Description |
+| --- | --- |
+| `system_cpu_percentage` | CPU percentage to see how much is being used (user, system), and how much is waiting for I/O (iowait), and how much is idle. |
+| `cgroup_mem_usage_MiB` | Memory usage of each cgroup. A cgroup usually corresponds to a Docker container. |
+| `cgroup_cpu_percentage` | CPU percentage of each cgroup. This lets you see which Docker container uses the most CPU. |
+| `app_cpu_utilization_percentage` | CPU usage of each process. This lets you see which processes are using the most CPU. |
+| `app_mem_usage_MiB` | Memory usage of each process. This lets you see which processes are using the most memory. |
+| `system_load_load` | System load average over 1, 5, and 15 minutes. |
+
+It also tracks metrics about your network, disk, and more.