README: Update Qemu instructions
README: Update Qemu instructions

Qemu has evolved since this text was written. We can now run skiboot on
upstream Qemu.

Signed-off-by: Joel Stanley <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@jms.id.au>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.ibm.com>

legoater/skiboot,qemu/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,shenki/skiboot,shenki/skiboot,qemu/skiboot,open-power/skiboot,qemu/skiboot,legoater/skiboot,qemu/skiboot,shenki/skiboot,stewart-ibm/skiboot,legoater/skiboot,stewart-ibm/skiboot,open-power/skiboot,stewart-ibm/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,legoater/skiboot,qemu/skiboot