dhi: add migration tip

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

Author: craig-osterhout

content/manuals/dhi/get-started.md

@@ -12,6 +12,18 @@ This guide shows you how to go from zero to running a Docker Hardened Image
 (DHI) using a real example. While the steps use a specific image as an
 example, they can be applied to any DHI.
 
+> [!TIP]
+>
+> You can keep using the same tools and workflows you already know when moving
+> to DHI from other images on Docker Hub, such as Bitnami public catalog images.
+> Note that Bitnami announced that its public catalog images will no longer be
+> available after September 29, 2025.
+>
+> In most cases, migrating is as simple as updating the image reference in your
+> configuration or commands. Start with this guide, then see the [migration
+> guide](./how-to/migrate.md) for more details and examples.
+
+
 ## Step 1: Sign up and subscribe to DHI for access
 
 To access Docker Hardened Images, your organization must [sign