docs: add Quick Start section to README

[SyncCore04]

Summary

Added a concise Quick Start section to the README, placed between "Demo & Documentation" and "Why You Should Use Springwolf". This gives new users a minimal, copy-paste-ready path to see Springwolf in action without leaving the README.

Changes

• Added "Quick Start" entry to the table of contents
• New section includes three steps:
  1. Add the Maven dependency — uses ${springwolf.version} placeholder with a comment pointing to the version badge in the Kafka plugin row below (avoids hard-coding a version that would go stale)
  2. Annotate existing listeners — shows a minimal @KafkaListener example, emphasizing that no extra code is required
  3. Start and view docs — lists the AsyncAPI JSON endpoint (/springwolf/docs) and the UI endpoint (/springwolf/asyncapi-ui.html)
• Ends with a link to the full quickstart guide on springwolf.dev for application.properties configuration details

Notes

• The section intentionally stays minimal — it complements (not replaces) the full documentation on springwolf.dev
• No existing content was modified or removed
• Version is not hard-coded, consistent with the rest of the README which uses dynamic badges

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