documentaton for correlation-id plugin

app/_data/plugins.yml

@@ -91,3 +91,7 @@
     - name: Loggly
       id: loggly
       info: Send request and response logs to Loggly
+
+    - name: Correlation ID
+      id: correlation-id
+      info: Correlate requests and responses using a unique ID

app/plugins/correlation-id.md

@@ -0,0 +1,48 @@
+---
+id: page-plugin
+title: Plugins - Correlation ID
+header_title: Correlation ID
+header_icon: /assets/images/icons/plugins/correlation-id.png
+breadcrumbs:
+  Plugins: /plugins
+nav:
+  - label: Getting Started
+    items:
+      - label: Configuration
+  - label: Usage
+    items:
+      - label: Logs
+---
+
+Correlate requests and responses using a unique ID.
+
+----
+
+## Configuration
+
+Configuring the plugin is straightforward. You can associate it with an [API][api-object] by executing the following request to your Kong server:
+
+```bash
+$ curl -X POST http://kong:8001/apis/{api}/plugins \
+    --data "name=correlation-id"
+```
+
+`api`: The `id` or `name` of the API that this plugin configuration will target
+
+form parameter      | required     | description
+---                 | ---          | ---
+`name`              | *required*   | The name of the plugin to use, in this case: `correlation-id`
+`header_name`       | *optional*   | The HTTP header name to use for the correlation ID. Defaults to `Kong-Request-ID`
+`generator  `       | *optional*   | The generator to use for the correlation ID. Accepted values are `uuid` (which generates a UUID for every request), or `uuid#counter` (which generates a UUID once per Nginx worker, and a count for every request). Defaults to `uuid#counter`.
+`echo_downstream`   | *optional*   | Whether to echo the header back to downstream (the API calller). Defaults to `false`.
+
+[api-object]: /docs/latest/admin-api/#api-object
+[configuration]: /docs/latest/configuration
+[consumer-object]: /docs/latest/admin-api/#consumer-object
+[faq-authentication]: /about/faq/#how-can-i-add-an-authentication-layer-on-a-microservice/api?
+
+----
+
+## Logs
+
+The correlation ID will not show up in the Nginx access or error logs. As such, we suggest you use this plugin alongside one of the Logging plugins.