README.md: document DataDog processor

README.md

@@ -1,3 +1,43 @@
 # Cirrus Webhooks Server
 
-Example of a simple server that processes webhook events from the Cirrus CI.
+Examples of the webhook event processors from the Cirrus CI.
+
+## Processors
+
+## DataDog
+
+This processor receives, enriches and streams Cirrus CI webhook events to DataDog.
+
+The simplest way to try this processor is to use Docker and [ngrok](https://ngrok.com/).
+
+First, you'll need to run the DataDog agent locally. The easiest way to do that would probably be [a Docker container](https://docs.datadoghq.com/containers/docker/?tab=standard), just don't forget to expose the DogStatsD port by adding the following argument to `docker run`:
+
+```
+-p 8125:8125/udp
+```
+
+Then, run the DataDog processor:
+
+```sh
+docker run -it --rm -p 8080:8080 ghcr.io/cirruslabs/cirrus-webhooks-server:latest datadog --dogstatsd-addr=host.docker.internal:8125
+```
+
+Note the `--dogstatsd-addr=host.docker.internal:8125`, it shows the DataDog processor where to find the DogStatsD daemon. In this case, it's on the Docker's host machine.
+
+Finally, [install](https://ngrok.com/download) and run `ngrok` to expose our DataDog processor's HTTP server to the internet:
+
+```sh
+ngrok http 8080
+```
+
+This will open the following TUI window:
+
+![](docs/ngrok-http-8080.png)
+
+You'll need to copy the forwarding address and set it in your organization's settings in the Cirrus CI app:
+
+![](docs/cirrus-ci-webhook-settings.png)
+
+Now you can run some tasks, and the corresponding audit events will appear shortly in your "Events Explorer":
+
+![](docs/datadog-webhook-event.png)