NEWS: Document virtio-pmem model
NEWS: Document virtio-pmem model

A few commits ago I've implemented virtio-pmem memory model.
Mention it in the news file.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

libvirt/libvirt,nertpinx/libvirt,libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,zippy2/libvirt,olafhering/libvirt,olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,zippy2/libvirt