docs: streamline README and move setup instructions

[tcheeric]

Summary

• strip badges and marketing copy from README
• move setup and dependency instructions into new docs/GETTING_STARTED.md

Testing

• mvn -q verify (fails: Could not find a valid Docker environment; see logs)

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https://chatgpt.com/codex/tasks/task_b_68a48db89dc883318bd941a41ac2046f

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✅ All modified and coverable lines are covered by tests.

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[Copilot]

Pull Request Overview

This PR streamlines the README by removing setup instructions and moving them to a dedicated getting started guide. The change improves documentation organization by separating high-level project overview from detailed setup procedures.

• Moved detailed Maven/Gradle setup instructions from README to new getting started guide
• Simplified README to focus on project overview with reference to setup documentation
• Removed redundant external project references from examples section

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
docs/GETTING_STARTED.md	New comprehensive setup guide with prerequisites, build instructions, and dependency configuration
README.md	Streamlined overview with reference to getting started guide and simplified examples section

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[Copilot]

The relative path '../nostr-java-examples' may not resolve correctly from the docs/ directory. Consider using './nostr-java-examples' or provide the full repository path for consistency with other documentation links.

Suggested change

	Examples are available in the [`nostr-java-examples`](../nostr-java-examples) module.
	Examples are available in the [`nostr-java-examples`](https://github.com/tcheeric/nostr-java/tree/main/nostr-java-examples) module.