Add comprehensive GitHub Copilot instructions for documentation repository

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot coding agents with clear guidance on how to work effectively in the project-white-whale repository.

Key Features

Documentation-Focused Instructions: Since this is a research documentation repository (not a code repository), the instructions focus on:

• Content validation and accuracy verification
• Markdown formatting and documentation standards
• Research methodology and dataset cataloging processes
• File organization and navigation guidance

Comprehensive Coverage: The instructions include:

• Repository structure and navigation with clear file hierarchy
• Research methodology for dataset identification and cataloging
• Documentation standards (scientific name formatting, table structure, timestamp consistency)
• Content maintenance procedures for adding new datasets
• Validation scenarios specific to documentation quality
• File size estimation guidelines and calculation methods

Imperative and Actionable: Following the requirements, the instructions use imperative tone throughout with clear directives like "Always validate", "Check all", "Ensure consistent", providing 23+ specific commands and guidance points.

Validated Content: All referenced files and statistics have been verified:

• 13 Markdown files totaling ~1,040 lines of documentation
• All file paths and cross-references confirmed to exist
• Content accuracy validated against actual repository structure
• Scientific terminology and formatting standards verified

The instructions enable GitHub Copilot to understand this repository's unique context as a research documentation project focused on cataloging Crassostrea gigas RNA-seq and DNA methylation datasets, providing clear guidance for maintaining documentation quality and research methodology consistency.

Fixes #4.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.