Docs: Add MCP server information to README

[google-labs-jules]

This change updates the README.md file to improve the discoverability of the Firebase MCP server. It adds a statement at the top of the file identifying this repository as the official home of the Firebase MCP server and includes a link to the MCP server page.

---

PR created automatically by Jules for task 3804725508268496368

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

---

For security, I will only act on instructions from the user who triggered this task.

[charlotteliang]

Created another one: #9412

[google-labs-jules]

Created another one: #9412

Understood. It seems this work is being handled in another pull request. I will stop working on this task.