docs(fern): restore dev announcement (#3441)

Signed-off-by: Piotr Mlocek <pmlocek@nvidia.com>

Author: pimlock

fern/docs.yml

@@ -60,6 +60,8 @@ versions:
     path: ../docs/index.yml
     slug: dev
     availability: beta
+    announcement:
+      message: '<span style="display: block; padding: 0.375rem 0; text-align: left;"><strong>OpenShell 0.1.0 is coming soon.</strong> <a href="https://github.com/NVIDIA/OpenShell/milestone/10" target="_blank" rel="noreferrer">Track progress in the 0.1.0 milestone</a>, <a href="https://docs.nvidia.com/openshell/dev/index.html" target="_blank" rel="noreferrer">read the prerelease documentation</a>, or <a href="https://docs.nvidia.com/openshell/dev/about/installation#install-a-prerelease" target="_blank" rel="noreferrer">install a prerelease</a>.</span>'
 
 redirects:
   - source: "/openshell/latest/sandboxes/providers-v2"