message: docs: fix cat script example
  `sudo cat > SOMEPATH <<EOF` won't work when user has no permission to
  write to SOMEPATH.
  Using `sudo tee SOMEPATH` instead.
diff: @@ -23,7 +23,7 @@ sudo cp nydusify containerd-nydus-grpc /usr/local/bin
  Nydus provides a containerd remote snapshotter `containerd-nydus-grpc` to prepare container rootfs with nydus formatted images. To start it, first save a `nydusd` configuration to `/etc/nydusd-config.json`:
  ```bash
  -$ sudo cat > /etc/nydusd-config.json << EOF
  +$ sudo tee /etc/nydusd-config.json > /dev/null << EOF
  {
  "device": {
  "backend": {
  