chore: add deprecation notice to README

[theashraf]

Summary

• Added a deprecation notice to the top of the README using GitHub > [!IMPORTANT] admonition syntax
• The notice directs users to @lottiefiles/dotlottie-react as the maintained successor, with links to npm and GitHub
• Appended "(Deprecated)" to the main title heading
• Added a horizontal rule (---) to separate the notice from the rest of the README

[changeset-bot]

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Latest commit: 54252ab

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