YOLOv8 export docs update (#1597)

Co-authored-by: dbogunowicz <97082108+dbogunowicz@users.noreply.github.com>
Co-authored-by: Mark Kurtz <mark.kurtz@neuralmagic.com>

src/sparseml/yolov8/README.md

@@ -62,13 +62,13 @@ To export the trained model to ONNX format, execute the appropriate
 CLI command and specify the path to the `.pt` model (`--model`):
 
 ```bash
-sparseml.ultralytics.export --model /.../model.pt
+sparseml.ultralytics.export_onnx --model /.../model.pt
 ```
 
 To look up optional arguments for the `export` command, run:
 
 ```bash
-sparseml.ultralytics.export -h
+sparseml.ultralytics.export_onnx --help
 ```
 
 The resulting exported model will be saved in the appropriate directory structure: