GPU usage in docs

https://github.com/InseeFrLab/torchTextClassifiers/blame/9a8b215dde66d6d549f4e479899edbb7c287fc12/docs/source/getting_started/quickstart.md#L262

`accelerator="gpu"` does not work for me, but `accelerator="cuda" ` works instead (as in `torch.device`).

Details of the error:

```
Traceback (most recent call last):
File "path/to/train_script.py", line xxx, in main
ttc.train(
~~~~~~~~~^
X_train,
^^^^^^^^
...<4 lines>...
verbose=True,
^^^^^^^^^^^^^
)
^
File path/to/torchTextClassifiers/torchTextClassifiers.py", line 401, in train
device = torch.device(training_config.accelerator)
RuntimeError: Expected one of cpu, cuda, ipu, xpu, mkldnn, opengl, opencl, ideep, hip, ve, fpga, maia, xla, lazy, vulkan, mps, meta, hpu, mtia, privateuseone device type at start of device string: gpu
```