Improve docs on Enhancing performance
Hi @albertvillanova, I hope you are doing well.

I am interested in this issue, is this still unresolved and open ?

The link you have provided in the above message directs to a webpage that does not exist.

Thanks and Regards #self-assign
In the ["Enhancing performance"](https://huggingface.co/docs/datasets/loading_datasets.html#enhancing-performance) section of docs, add specific use cases:
- How to make datasets the fastest
- How to make datasets take the less RAM
- How to make datasets take the less hard drive mem

cc: @thomwolf 
