Review Data Input Pipeline guides

[melissawm]

Description

This PR includes a review of the recently-added Data Input Pipeline guides (follow-up to https://github.com/AI-Hypercomputer/maxtext/pull/2244)

Some specific changes, including touching some files outside of the Data Input Pipeline guides:

• Documents must always start with a H1 header, and the subsequent headers must be sequential (i.e. an error will be raised in the ReadTheDocs/Sphinx build if a H1 header is followed by a H3 header, skipping a H2).
• I added a few links I thought were appropriate, but I will flag them below.
• To be able to appear in the documentation, all documents must appear exactly once in a Table of Contents. In this case, I added a "toctree" directive to the guides/data_input_pipeline.md file but it is hidden. This means it does not appear in the rendered documentation page, but generates subsections for the child documents. See the screenshot below:

Tests

I have built the documentation pages locally to verify that it works.

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• [x] I have performed a self-review of my code.
• [x] I have necessary comments in my code, particularly in hard-to-understand areas.
• [x] I have run end-to-end tests tests and provided workload links above if applicable.
• [x] I have made or will make corresponding changes to the doc if needed.

[melissawm]

This is ready for another round of review, thanks @aireenmei !

[github-actions[bot]]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed soon if no further activity occurs. Thank you for your contributions.

[github-actions[bot]]

This PR was closed because it has been inactive for a while. Please reopen it if you are still working on it.

[melissawm]

Hi all, let me know if I can follow-up on this. Thanks

[hengtaoguo]

Hi @melissawm could you squash into one commit and sync to head?

[melissawm]

This is now rebased and squashed. Thanks!

[aireenmei]

Not sure why this PR is still open, I submitted the corresponding internal cl yesterday (https://github.com/AI-Hypercomputer/maxtext/commit/af29099b2209643e31619fd842cf646d82ca2b82)