Updates installation page organization and contents

[melissawm]

Description

Updates installation page contents and structure, with focus on complying with the Google Technical Writing Guidelines and team feedback.

Also splits the "How to update requirements" to a separate page under a "development" folder, containing documentation on how to contribute.

Tests

Documentation builds locally.

Checklist

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

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• [N/A] I have necessary comments in my code, particularly in hard-to-understand areas.
• [N/A] I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[melissawm]

The docs build here will pass once #3247 is merged.

[melissawm]

Just updated this PR with the following changes:

• Reorganized the "Update dependencies" guide so that the summary steps match the detailed steps. Please let me know if the steps are correct;
• Added a target to the "From source" section of the "Install MaxText" page so we can link to it directly internally;
• Rebased the contents of the PR to match the main branch.

Let me know if you have further feedback. Thanks!

[melissawm]

I have rebased and squashed this PR to resolve some conflicts. Let me know if you have further comments.

cc @jacoguzo