"Nydus is an OCI/Docker-compatible ..." is slightly misleading

[AkihiroSuda]

buildkit/docs/nydus.md

Line 3 in e853c88

Nydus is an OCI/Docker-compatible accelerated image format provided by the Dragonfly [image-service](https://github.com/dragonflyoss/image-service) project, which offers the ability to pull image data on-demand, without waiting for the entire image pull to complete and then start the container. It has been put in production usage and shown vast improvements to significantly reduce the overhead costs on time, network, disk IO of pulling image or starting container.

This is slightly misleading as the image layer blobs are in a different format