scsi: Document necessary qemu config

We are currently hardcoding the queue number to 3 (2 control + 1 data).
QEMU will attempt to pick its own values if we do not configure the
number explicitly.

Author: Erik Schilling

crates/scsi/README.md

@@ -14,7 +14,7 @@ Run QEMU:
 
 ```
 qemu-system-x86_64 ... \
-  -device vhost-user-scsi-pci,chardev=vus \
+  -device vhost-user-scsi-pci,num_queues=1,chardev=vus \
   -chardev socket,id=vus,path=/tmp/vhost-user-scsi.sock \
   # must match total guest meory
   -object memory-backend-memfd,id=mem,size=384M,share=on \