Update quicktour docs to showcase the use of truncation

[navjotts]

What does this PR do?

Currently, running the tokenizer batch example on https://huggingface.co/transformers/quicktour.html gives an error

Asking to truncate to max_length but no maximum length is provided and the model has no predefined maximum length. Default to no truncation.

This PR fixes the above by passing the max_length param explicitly (instead of depending on it having a default, which might not be the case for all models).

The fix also adds clarity to the statement in the docs above this example

If your goal is to send them through your model as a batch, you probably want to pad them all to the same length, truncate them to the maximum length the model can accept and get tensors back

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).

Who can review?

@sgugger

[sgugger]

Thanks, this looks good indeed!