docs: add missing iothread stats docs in domstats
docs: add missing iothread stats docs in domstats

Signed-off-by: Nikolay Shirokovskiy <7fa0e2698a05be944b362bdf5d7736c0162e16c9@virtuozzo.com>
Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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