versions: Add default initrd information

Add information about the default initrd.

Signed-off-by: Jose Carlos Venegas Munoz <[email protected]>

versions.yaml

@@ -72,6 +72,15 @@ assets:
     meta:
       image-type: "clearlinux"
 
+  initrd:
+    description: |
+      Root filesystem initrd used to boot the guest virtual
+      machine.
+    url: "https://github.com/kata-containers/osbuilder"
+    meta:
+      base-os: "alpine"
+      os-version: "3.7"
+
   kernel:
     description: "Linux kernel optimised for virtual machines"
     url: "https://cdn.kernel.org/pub/linux/kernel/v4.x/"