Add comprehensive NAS documentation to Dev-Journal

[Copilot]

This PR adds comprehensive documentation about Network Attached Storage (NAS) to answer the question "What is NAS?" and establishes a structured approach for organizing topics in the Dev-Journal repository.

Changes Made

New Documentation Structure:

• Created a topics/ directory to organize learning materials
• Added topics/NAS.md with 179 lines of comprehensive NAS documentation
• Updated README.md to reference the new structure and provide navigation

NAS Documentation Coverage:
The new NAS guide provides a complete educational resource covering:

• Fundamentals: Definition, architecture, and core characteristics
• Technical Details: Access methods, RAID configurations, and performance factors
• Practical Applications: Use cases for home users, small business, and enterprise
• Product Landscape: Popular solutions across consumer, enterprise, and open-source categories
• Comparative Analysis: Detailed comparisons with SAN, DAS, and cloud storage solutions
• Security & Future: Security considerations and emerging trends

Repository Organization:

• Established a scalable structure for future topic additions
• Added clear navigation and usage guidelines in the README
• Maintained the repository's educational purpose while improving organization

The documentation serves as both a comprehensive answer to the NAS question and a template for future topic additions to the dev journal.

Fixes #17.

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