doc: zh_CN: add translation for virtiofs

Translate virtiofs.rst in Documentation/filesystems/ into Chinese.

Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Wang Wenhu <wenhu.wang@vivo.com>
Link: https://lore.kernel.org/r/20200316110143.97848-2-wenhu.wang@vivo.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>