Add user guide to update MaxText dependencies with seed-env

[bvandermoon]

Description

Guide to update MaxText requirements using the new seed-env setup.

The main idea is to:

1. Update base requirements
2. Pass base requirements file to seed-env tool
3. seed-env tool generates requirements files with lower bounds
4. Commit generated files to MaxText

Tests

N/A - documentation only

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.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• 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.

[khatwanimohit]

LGTM