Add 'Part of the Pydantic Stack' footer to README

[strawgate]

Adds a short "Part of the Pydantic Stack" footer to the README so readers can discover the other products in one place.

[coderabbitai]

Note

Reviews paused

It looks like this branch is under active development. To avoid overwhelming you with review comments due to an influx of new commits, CodeRabbit has automatically paused this review. You can configure this behavior by changing the reviews.auto_review.auto_pause_after_reviewed_commits setting.

Use the following commands to manage reviews:

• @coderabbitai resume to resume automatic reviews.
• @coderabbitai review to trigger a single review.

Use the checkboxes below for quick actions:

• ▶️ Resume reviews
• 🔍 Trigger review

📝 Walkthrough

Walkthrough

A new "Part of the Pydantic Stack" section is inserted into README.md between the existing "Contributing" and "License" sections. It contains three bullet-point links pointing to Pydantic AI, Pydantic Logfire, and Pydantic AI Gateway. No code or exported entities are modified.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and accurately describes the main change—adding a 'Part of the Pydantic Stack' footer section to the README.
Description check	✅ Passed	The description is directly related to the changeset, explaining the purpose of adding the footer to help readers discover other Pydantic Stack products.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch billea/readme-pydantic-stack-footer

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}