✨ Set up Copilot instructions for devcontainer features repository with versioning guidelines

[Copilot]

Adds comprehensive Copilot coding agent instructions to help contributors understand and work effectively with this devcontainer features repository.

The new .copilot-instructions.md file provides detailed guidance covering:

Repository Context

• Clear explanation of devcontainer features and their purpose in GitHub Codespaces
• Complete documentation of the repository structure (/src/, /test/, workflows)
• Overview of all current features with descriptions

Development Guidelines

• Step-by-step process for creating new features
• Feature implementation best practices (error handling, logging, idempotency)
• Cross-platform compatibility requirements (Ubuntu, Debian, Mariner Linux)
• Semantic versioning guidelines with SemVer specification for MAJOR, MINOR, and PATCH versions
• Version management process for updating devcontainer-feature.json during changes

Testing Framework

• Comprehensive testing patterns using devcontainer CLI
• Test execution commands for different scenarios
• Integration testing with _global test scenarios

CI/CD Documentation

• Explanation of automated testing workflows (test-pr.yaml, test-all.yaml)
• Release process and versioning guidelines
• Path-based change detection for efficient testing

Code Quality Standards

• Shell script best practices and common patterns
• JSON configuration guidelines
• Security considerations and debugging techniques

Documentation Standards

• Clarifies that README.md and NOTES.md files are auto-generated and should never be edited manually
• Updated Pull Request process to include mandatory version updates following semantic versioning

This documentation follows the best practices for Copilot coding agent and will help both new contributors and AI coding assistants understand the codebase structure, conventions, and development workflows specific to devcontainer features.

Fixes #78.

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[markphip]

@copilot looks good aside from comment that we should add something about maintaining the version as part of the update process.

Also each feature has a NOTES.md with any special notes that should appear in the README.md. That file is generated and should never be edited

[markphip]

@copilot Can we add something about semantic versioning and updating the version in devcontainer-feature.json as part of making a change

[Copilot]

Added semantic versioning section with SemVer guidelines and updated the Pull Request Process to include version updates as step 3. The changes include guidance on when to increment MAJOR, MINOR, or PATCH versions and requirement to update the version field in devcontainer-feature.json. Commit be35388

[Copilot]

@copilot looks good aside from comment that we should add something about maintaining the version as part of the update process.

Also each feature has a NOTES.md with any special notes that should ap...

Added comprehensive version management information including semantic versioning guidelines and updated the Feature Structure section to clarify that both README.md and NOTES.md files are auto-generated and should never be edited manually. Also enhanced the Pull Request Process to include version updates as a required step. Commit be35388