task #28910367
commit 2d1d25d0a224dcd2021004d52342fc1727ccd85f upstream

Add information about the new "virtiofs" file system.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: NLiu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>