[libvirt] Update the release note of released version

[Michal Privoznik]

On 10/9/19 4:44 PM, Han Han wrote:
> Hi,
> Although libvirt-5.8 is released, however some features or improvement like
> "slirp helper process" are missing in release note now. Can I update the
> news.xml
> even after v5.8 ?

That would only affect our web page and future releases. Unfortunately, 
we can't change the released .tar.xz file.

Michal