Add 1-page PDF cover letter for non-expert audience

[Copilot]

This PR addresses the need for accessible documentation by creating a comprehensive 1-page PDF cover letter specifically designed for non-expert audiences including high school students, undergraduate non-CS majors, educators, professionals in other domains, and the general public.

What's Added

LLM4ChipDesign_Cover_Letter.pdf - A professionally formatted, single-page cover letter that includes:

• Clear target audience identification - Explicitly states who the materials are for (high school students, non-CS undergraduates, educators, professionals from other fields, general public)
• Time investment guide - Detailed table showing expected time commitments for different material types:
  • Quick overview: 5 minutes
  • Interactive tutorials: 30-90 minutes each
  • Research papers: 20-45 minutes each
  • Presentation slides: 15-30 minutes each
  • Video presentations: 45-60 minutes each
  • Complete collection: 10-20 hours total
• Accessible content description - Explains how AI/LLMs are revolutionizing chip design in plain language
• Featured research areas - Highlights key projects like AutoChip, C2HLSC, hardware testing automation, and security applications
• Getting started guidance - Points readers to interactive Colab tutorials as the best entry point

Design Considerations

The cover letter uses:

• Professional formatting with clear visual hierarchy
• Non-technical language that doesn't assume prior CS/EE knowledge
• Emojis and visual elements to make it approachable
• Structured layout that's easy to scan and read
• Reference to the repository URL for easy access

This document serves as an entry point for anyone curious about the intersection of AI and hardware design, regardless of their technical background.

Also includes a .gitignore file to maintain clean repository structure.

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