chore: Add Bluesky badge to README (#53616)

Summary:
Add Bluesky badge to README.

## Changelog:

[INTERNAL][ADDED] Add Bluesky badge to README

Pull Request resolved: https://github.com/facebook/react-native/pull/53616

Test Plan:
The updated README has been checked out on the PR branch.

## Preview:

<img width="1880" height="746" alt="Screenshot 2025-09-05 at 13 00 34" src="https://github.com/user-attachments/assets/dc1dfa9c-9e08-449d-82b8-dcb92ae92268" />

Reviewed By: cipolleschi

Differential Revision: D81909921

Pulled By: cortinico

fbshipit-source-id: b5fa79f152f126944bc1c31c8fbb86889f0f25db