Update pytorch-model.md with a new troubleshooting help

[antimora]

Pull Request Template

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Changes

Update pytorch import book section on troubleshooting

Testing

Rendered the book

[laggui]

The new section is superfluous.

The first section after the intro is already How to export a PyTorch model

and the example clearly shows the state_dict() being saved.

if __name__ == "__main__":
    torch.manual_seed(42)  # To make it reproducible
    model = Net().to(torch.device("cpu"))
    model_weights = model.state_dict()
    torch.save(model_weights, "conv2d.pt")

Instead of adding a whole new section even further down, I would simply add a sentence in the first section to highlight that only the state dict should be saved.

[laggui]

Makes more sense now! Steps flow naturally.

Two minor comments, then will be good to go!