offload: add trial credit expiration note (#23252)

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## Description

Add temporary note about free trial credit expiration.

https://deploy-preview-23252--docsdocker.netlify.app/offload/usage/

## Related issues or tickets

DCL-669

## Reviews

<!-- Notes for reviewers here -->
<!-- List applicable reviews (optionally @tag reviewers) -->

- [ ] Technical review
- [ ] Editorial review
- [ ] Product review

Signed-off-by: Craig <[email protected]>

Author: craig-osterhout

content/manuals/offload/usage.md

@@ -8,6 +8,13 @@ keywords: cloud, usage, cloud minutes, shared cache, top repositories, cloud bui
 
 {{< summary-bar feature_name="Docker Offload" >}}
 
+> [!NOTE]
+>
+> All free trial credits granted for the Docker Offload Beta expire after 90
+> days from the time they are granted. To continue using Docker Offload after
+> your credits expire, you can enable on-demand usage at [Docker Home
+> Billing](https://app.docker.com/billing).
+
 ## Docker Offload billing
 
 For Docker Offload, you can view and configure billing on the **Docker Offload**