What's the document you plan to update? Why? Please describe

The current official documentation lacks an introduction to migratable RWX volumes, which leads to user confusion, either not knowing how to use Longhorn migratable RWX volumes with KubeVirt or mistakenly setting spec.migratable to true for non-migratable RWX volumes. To reduce support efforts and improve user understanding, we should provide detailed guidance on migratable RWX volumes in the documentation.

Additional context