DOC: Add more specific GPU examples to System Requirements in README.md #395

[abhishekkamble12]

Summary
Add concrete GPU examples for the 8GB+ and 24GB+ VRAM recommendations in the System Requirements section.
Improve readability by using “VRAM” terminology consistently.
Rationale
New users can quickly gauge if their hardware meets the model requirements without looking up GPU memory specs elsewhere.
Changes
Update README.md System Requirements text to include example GPUs (RTX 3060 for 8GB+, RTX 4090 and RX 7900 XTX for 24GB+).
Testing
Not applicable (documentation-only change).

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