message: readme: tiny refine of readme introduction part
diff: @@ -10,10 +10,10 @@ The following benchmarking result shows the performance improvement compared wit
  Nydus' key features include:
  -- Container images are downloaded on demand in chunks to boost container startup
  -- Chunk level data de-duplication among layers in a single repository to reduce storage cost
  +- Container images may be downloaded on demand in chunks to boost container startup
  +- Chunk level data de-duplication among layers in a single repository to reduce storage, transport and memory cost
  - Flatten image metadata and data to remove all intermediate layers
  -- Deleted(whiteout) files in certain layer aren't packed into nydus image, therefore, image size can be reduced
  +- Deleted(whiteout) files in certain layer aren't packed into nydus image, therefore, image size may be reduced
  - E2E image data integrity check. So security issues like "Supply Chain Attach" can be avoided and detected at runtime
  - Compatible with the OCI artifacts spec and distribution spec, so nydus image can be stored in a regular container registry
  - Integrated with CNCF incubating project Dragonfly to distribute container images in P2P fashion and mitigate the pressure on container registries
  