[bnb] Minor modifications
# What does this PR do?

Addressing the request from https://github.com/huggingface/transformers/pull/17901 to refactor the documentation a little bit and fixes small details in the bnb PR. 

- Fixing documentation
- Added useful troubleshooting document for more efficient debugging
- Updated the `Dockerfile` with the correct `bitsandbytes` version

cc @stas00 @ydshieh 

_The documentation is not available anymore as the PR was closed or merged._<|||||>You could also read the rendered doc (not GitHub page) below

https://moon-ci-docs.huggingface.co/docs/transformers/pr_18631/en/perf_train_gpu_one#efficient-training-on-a-single-gpu
(toward the end)<|||||>@ydshieh do you think we should keep the version `0.31.8` on the Dockerfile since we know it's the version that works 🤔 <|||||>> @ydshieh do you think we should keep the version `0.31.8` on the Dockerfile since we know it's the version that works 🤔

So far let's not add this. If the newer versions constantly break things, we can ping a particular versions.<|||||>Great works for me!<|||||>Great thanks! 
Do you think that we can merge it for now? I am especially interested in seeing if the changes in the `Dockerfile` would change anything (theoretically no, but we are using `bitsandbytes==0.31.5` on the Dockerfile and the latest verison is the `0.31.8`). For the rest since it's related to documentation I think we can always re-iterate.
Perhaps I can open a separate PR just to change the Dockerfile?<|||||>If you feel it's complete and want to merge it, go for it. We can always improve it later.<|||||>Thanks a lot!
Just went through a final pass, looks good to me!<|||||>@younesbelkada, I have just realized that this PR added to the wrong perf doc. This new feature is inference only and thus ideally should go into the inference doc and not training. Probably the many-gpu one. https://github.com/huggingface/transformers/blob/main/docs/source/en/perf_infer_gpu_many.mdx

Thanks.<|||||>No problem at all and sorry for the inconvenience, will re-open a PR for that!<|||||>I have addressed a PR at: https://github.com/huggingface/transformers/pull/18671 ! 