dhi: add to homepage (#22923)

<!--Delete sections as needed -->

## Description

Add DHI card to homepage.
Refine wording as it's not just "base" images.

## Related issues or tickets

<!-- Related issues, pull requests, or Jira tickets -->

## Reviews

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

- [ ] Editorial review

Signed-off-by: Craig <craig.osterhout@docker.com>

content/_index.md

@@ -14,6 +14,17 @@ grid:
         url: "/desktop/use-desktop/"
       - text: "Release notes"
         url: "/desktop/release-notes/"
+  - title: Docker Hardened Images
+    icon: /icons/dhi.svg
+    description: |
+      Secure, minimal images for trusted software delivery.
+    links:
+      - text: "Overview"
+        url: "/dhi/"
+      - text: "Quickstart"
+        url: "/dhi/get-started/"
+      - text: "Use an image"
+        url: "/dhi/how-to/use/"
   - title: Docker Engine
     icon: developer_board
     description: |

content/manuals/_index.md

@@ -50,7 +50,7 @@ params:
     icon: /icons/Whale.svg
     link: /desktop/
   - title: Docker Hardened Images
-    description: Secure, minimal base images for trusted software delivery.
+    description: Secure, minimal images for trusted software delivery.
     icon: /icons/dhi.svg
     link: /dhi/
   - title: Build Cloud