docs: add real-world example to Observer pattern README

[MiguelAntonioRS]

What has been done

Added a new "Real-World Example" section to the Observer pattern README file.

Why this change

To provide a practical explanation of how the Observer pattern is applied in modern Java applications, helping readers better understand its use in real projects.

How to test

Open the file observer/README.md and verify that the new section appears at the end of the document.

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Hacktoberfest contribution 🎃

[github-actions[bot]]

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• 9088a41: docs: add real-world example to Observer pattern README

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[MiguelAntonioRS]

Hi, the CI check "Presubmit.ai / review" failed because the workflow seems to be missing its LLM_API_KEY secret and references a non-existent model (gemini-1.5-flash).
This issue appears unrelated to my documentation change.

Could you please review the PR manually?
Thanks and happy Hacktoberfest! 🎃

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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