docs: fix PyTorch compression command (#4780)

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## Summary by CodeRabbit

- **Documentation**
- Updated the command example for compressing a PyTorch model to
explicitly include the `--pt` flag.

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Signed-off-by: Jinzhe Zeng <[email protected]>

Author: njzjz

doc/freeze/compress.md

@@ -77,7 +77,7 @@ dp compress -i graph.pb -o graph-compress.pb
 :::{tab-item} PyTorch {{ pytorch_icon }}
 
 ```bash
-dp compress -i model.pth -o model-compress.pth
+dp --pt compress -i model.pth -o model-compress.pth
 ```
 
 :::