Update README to reflect relocatable packages as primary usage pattern

[Copilot]

Summary

Successfully updated README.md to reflect modern Scylla CCM usage with relocatable packages as the primary method.

Completed Tasks

• Understand current README structure and relocatable package usage in code
• Update README introduction to reflect Scylla CCM fork focus
• Replace outdated Cassandra-centric examples with modern Scylla relocatable package examples
• Add clear documentation for version formats (release:X.X.X and unstable/branch:timestamp)
• Update installation instructions to match current build system (UV)
• Add relocatable package usage patterns with examples
• Update Docker cluster examples
• Clean up and remove outdated Cassandra-specific sections
• Verify examples work with current code
• Address code review feedback (fix timestamp examples)
• Remove PyPI and Homebrew sections (this fork doesn't publish to them)
• Final validation complete

Key Changes

1. Scylla-First Approach: Reorganized to prioritize Scylla usage while maintaining Cassandra support
2. Relocatable Packages: Added comprehensive section explaining version formats and custom package options
3. Modern Examples: All version examples updated to 2024.2+ and current timestamp formats
4. Better Structure: Added Quick Start, Common Commands, and programmatic usage sections
5. Accurate Documentation: All examples validated against actual code in scylla_repository.py and cmds/cluster_cmds.py
6. Installation: Removed PyPI and Homebrew sections (fork-specific change)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Change README.md to reflect usage of relocatable packages</issue_title>
<issue_description>Right now the README file is totally out of date</issue_description>

<agent_instructions>Suggest updates yo the readme to match it as much as possible to the code and to scylla usage</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Change README.md to reflect usage of relocatable packages #176

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