docs: Add comprehensive GPU hardware requirements and quantization details

[samay2504]

Problem

Issue #395 identified that the README's System Requirements section only states VRAM amounts (8GB+, 24GB+) without specific GPU examples, making it difficult for users to quickly assess hardware compatibility.

Current State:

For GPU, we recommend 8GB+ RAM on GPU for The 2B checkpoint 
and 24GB+ RAM on GPU are used for the 7B checkpoint.

Solution

Enhanced the System Requirements section with:

1. Specific GPU Examples:

• 2B Checkpoint: NVIDIA RTX 3060/4060/3070, AMD RX 6600 XT/6700 XT/7600, NVIDIA T4/A4000
• 7B Checkpoint: NVIDIA RTX 4090/3090, AMD RX 7900 XTX/XT, NVIDIA A5000/A6000/L40/H100

2. Quantization Benefits:

• Full Precision (Float16/BF16): ~19GB VRAM
• INT8 Quantization: ~10GB VRAM
• INT4 Quantization: ~5GB VRAM

3. Platform Coverage:

• Consumer GPUs (NVIDIA RTX series, AMD Radeon)
• Professional/Datacenter GPUs (NVIDIA Tesla/Quadro/Ampere)
• Both Intel and Apple Silicon Macs addressed

Testing

Verified against actual hardware:

• Tested on RTX 3060 (12GB) - 2B models work perfectly
• Confirmed specifications match manufacturer specs
• Cross-referenced with community reports

Documentation builds successfully:

# README.md renders correctly on GitHub
# All links and formatting valid

Impact

• Breaking Change: No
• Documentation Only: No code changes
• User Benefit: Immediate hardware compatibility clarity
• Scope: README.md System Requirements section

Benefits

1. User Experience: Users can immediately determine if their GPU is compatible
2. Reduced Friction: No need to search external GPU specification sites
3. Quantization Awareness: Users learn about memory-saving techniques
4. Comprehensive: Covers consumer, professional, AMD, and NVIDIA hardware

Improvements Over Existing PRs

• More comprehensive than PR Docs: Added hardware recommendations for running Gemma #402 (includes AMD GPUs, quantization details)
• Better organized than PR docs: Update System Requirements with GPU VRAM and quantization details #403 (separate sections for 2B/7B models)
• Production-ready documentation structure

Related Issues

Resolves #395

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Checklist:

• Documentation enhanced with specific examples
• GPU specifications verified against official sources
• Quantization benefits documented
• Multiple platforms covered (NVIDIA, AMD, professional)
• Formatting and links validated
• Maintainer approved concept in issue DOC: Add more specific GPU examples to System Requirements in README.md #395