Improved message to suppress errors in _dynamo/exc.py (#97345)

If user adds simply to their code:
```python
import torch

torch._dynamo.config.suppress_errors = True
```
they will get:
```
AttributeError: module 'torch' has no attribute '_dynamo'
```

Pull Request resolved: https://github.com/pytorch/pytorch/pull/97345
Approved by: https://github.com/zou3519, https://github.com/kit1980

torch/_dynamo/exc.py

@@ -187,6 +187,7 @@ def augment_exc_message(exc, msg="\n"):
         msg += (
             "\n\n"
             "You can suppress this exception and fall back to eager by setting:\n"
+            "    import torch._dynamo\n"
             "    torch._dynamo.config.suppress_errors = True\n"
         )