Add GitHub Copilot instructions file

[Copilot]

Creates .github/copilot-instructions.md to provide AI-assisted development context for this repository.

Contents

• Project context: Bash wrapper for Git Sizer analyzing repository bloat and large files
• Bash conventions: Function style, variable quoting, error handling, OS detection patterns
• Architecture: Parallel processing design (&/wait), working directory structure, cleanup flow
• Testing: Platform compatibility requirements (Linux/macOS/Windows), manual test scenarios
• Dependencies: Git Sizer v1.5.0 (referenced at clean.sh:8,11,14), standard Unix utilities
• Maintenance: Version update locations, clarifying questions policy

File extracts conventions from existing clean.sh implementation and aligns with educational tone of README.md.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create Copilot Instructions File</issue_title>
<issue_description>## Objective
Check if a Copilot instruction file exists in the repository, and if not, create one with best practices.

Tasks

• Search for existing Copilot instruction files in the following locations:
  • .github/copilot-instructions.md
  • .github/copilot.md
  • Root-level instruction files
• If no file exists, create .github/copilot-instructions.md with:
  • Project-specific context and conventions
  • Coding standards and style guidelines
  • Testing requirements
  • Documentation expectations
  • Architecture patterns used in the project
  • Any clarifying questions policy (e.g., "ask clarifying questions before building plans")
• Create a pull request with the new instruction file

Acceptance Criteria

• Instruction file is placed in .github/copilot-instructions.md
• File contains relevant, actionable guidelines for the project
• PR is created and ready for review</issue_description>

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

• Fixes Create Copilot Instructions File #1

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