Update README with project purpose and description

[Copilot]

Enhanced README.md to provide clear context about the repository's purpose as a test environment for GitHub Copilot coding agent.

Changes

• Expanded description to explicitly state this is a test repository for GitHub Copilot coding agent
• Added Purpose section explaining usage as a sandbox for validating agent functionality and workflows
• Improved formatting and structure for better readability

Original prompt

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This section details on the original issue you should resolve

<issue_title>Test: Update README with project purpose</issue_title>
<issue_description>## Task

Update README.md with a description of this repository's purpose.

Requirements

1. Add a brief description stating this is a test repo for Copilot coding agent
2. Keep it simple

Acceptance Criteria

• README.md has meaningful content</issue_description>

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

• Fixes Test: Update README with project purpose #1

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