[docs] Quicktour

[stevhliu]

This PR updates the Quicktour to focus more on the library's core offerings:

➕ organizes the Quicktour around the three main features: unified launcher, Accelerator class, and Big Model Inference
➕ new tutorials for Execution process and TPU training
➕ adds save Transformer models from Accelerator API page to same section with saving/loading models in Add Accelerate to your code tutorial
➕ adds on_local_main_process, on_main_process, on_process, and on_local_process from Accelerator API page to the Execution process docs
➖ removes the "Common modifications of the base case" section because all these different scenarios can be overwhelming for a new user and because it is not necessarily needed to help users start quickly. These sections will be integrated as a part of the tutorials, and I'll add links to redirect users there from the Quicktour. Only exception is the Launching distributed training from a notebook because there is already a tutorial for that.

• move content from the "Common modifications of the base case" section into the Tutorials

[HuggingFaceDocBuilderDev]

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[muellerzr]

First pass: quicktour only

[muellerzr]

I feel like this whole doc is just a repeat of https://moon-ci-docs.huggingface.co/docs/accelerate/pr_2456/en/concept_guides/deferring_execution no? I don't think it makes sense to have it here in the base tutorials.

[stevhliu]

I think the "Deferring execution" guide shows examples of when to use main_process_first or wait_for_everyone such as downloading a dataset or saving/loading a state dict. This doc has a broader scope and introduces the different execution scenarios you should consider (ie, do you want to execute on one process, on a specific process).

I think introducing these types of scenarios in the tutorials gives users a nice basic understanding of how to apply it to the more specific examples, such as the ones showcased in the Deferring execution doc. Let me know what you think! 🙂

[muellerzr]

Thanks for the rework!