Update the hf_ptq.yaml (#1175)

### What does this PR do?

Type of change: Bug fix

Fix the CLI override example comment in
`tools/launcher/examples/Qwen/Qwen3-8B/hf_ptq.yaml` by adding a missing
`--` (double-dash separator) to the `task_0.args` override.

Without the `--` separator, the `--quant` flag would be parsed as an
argument to the launcher/download script rather than being passed
through to the PTQ script (`huggingface_example.sh`). This aligns the
comment example with the actual `task_0.args` definition in the YAML
(line 42), which already correctly includes the `--` separator.

### Testing

Verified the comment now matches the actual args format used in the YAML
config.

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Updated example configuration to correct command-line parameter
formatting in commented usage example.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Chenjie Luo <chenjiel@nvidia.com>

Author: cjluo-nv

tools/launcher/examples/Qwen/Qwen3-8B/hf_ptq.yaml

@@ -20,7 +20,7 @@
 # Override model/quant via CLI:
 #   uv run launch.py --yaml examples/llm_ptq/hf_ptq.yaml \
 #       pipeline.global_vars.hf_model=Qwen/Qwen3-8B \
-#       pipeline.task_0.args='[--model,<<global_vars.hf_local>>Qwen/Qwen3-8B,--quant,nvfp4]' \
+#       pipeline.task_0.args='[--model,<<global_vars.hf_local>>Qwen/Qwen3-8B,--,--quant,nvfp4]' \
 #       --yes
 
 job_name: hf_ptq_nvfp4