message: nydusify: Fix nydusify help messages
  1. The "--merge-platform" flag in nydusify convert no longer need to push OCIv1 image first.
  2. Fix wrong indentation in Version prompt.
diff: @@ -315,7 +315,7 @@ func main() {
  &cli.BoolFlag{
  Name: "merge-platform",
  Value: false,
  - Usage: "Generate an OCI image index with both OCI and Nydus manifests for the image, please ensure that the OCI image exists in the target repository",
  + Usage: "Generate an OCI image index with both OCI and Nydus manifests for the image",
  EnvVars: []string{"MERGE_PLATFORM"},
  Aliases: []string{"multi-platform"},
  },
  