message: Update nydusd doc for bootstrap creation
  Add a link for nydus-image.md as a reference.
diff: @@ -24,6 +24,7 @@ cat /path/to/config-localfs.json
  ```
  ### Run With FUSE
  +If no `/path/to/bootstrap` is available, please refer to [nydus-image.md](https://github.com/dragonflyoss/image-service/blob/master/docs/nydus-image.md) for more details.
  ``` shell
  sudo nydusd \
  @@ -34,6 +35,7 @@ sudo nydusd \
  ```
  ### Run With Virtio-FS
  +If no `/path/to/bootstrap` is available, please refer to [nydus-image.md](https://github.com/dragonflyoss/image-service/blob/master/docs/nydus-image.md) for more details.
  Virtio-fs is supported by both [QEMU](https://www.qemu.org/) and [Cloud-hypervisor](https://github.com/cloud-hypervisor/cloud-hypervisor). To run `nydusd` with virtio-fs support, first start it with `--sock` option to expose a virtio-fs socket endpoint.
  