fix(cli-docs): add --message flag to push publish, update --channel description

src/pages/docs/cli/push/publish.mdx

@@ -30,7 +30,11 @@ A raw JSON recipient object. Exclusive with `--device-id` and `--client-id`.
 
 ### `--channel` <a id="channel"/>
 
-The target channel name. Publishes a push notification via the channel using `extras.push`. Ignored if `--device-id`, `--client-id`, or `--recipient` is also provided.
+The target channel name. Publishes a push notification via the channel using `extras.push`. Ignored if `--device-id`, `--client-id`, or `--recipient` is also provided. Use together with `--message` to publish a realtime message on the channel alongside the push notification.
+
+### `--message` <a id="message"/>
+
+Realtime message data to include alongside the push notification. Accepts either plain text or raw JSON, and the value is used as the realtime message `data` payload rather than a full message object. Only applies when publishing via `--channel`.
 
 ### `--title` <a id="title"/>
 
@@ -171,6 +175,22 @@ ably push publish --channel my-channel --payload '{"notification":{"title":"Hell
 ```
 </Code>
 
+Publish a push notification to a channel with a realtime message string:
+
+<Code>
+```shell
+ably push publish --channel my-channel --title Hello --body World --message 'Hello from push'
+```
+</Code>
+
+Publish a push notification to a channel with a realtime message JSON payload:
+
+<Code>
+```shell
+ably push publish --channel my-channel --title Hello --body World --message '{"event":"push","text":"Hello"}'
+```
+</Code>
+
 Publish to a channel using a payload from a file:
 
 <Code>