Update Docs

Author: technowhizz

roles/iommu/README.md

@@ -4,6 +4,10 @@
 
 - `iommu_pt`: Default true, Configure passthrough mode, which doesn't require DMA translation.
 
+## Host Vars
+
+- `vfio_pci_ids`: Can optionally be set with the pci id of the device to pass-through.
+
 ## Example playbook
 
 ```