[DOC] Minor grammar and clarity improvements in README.md

Hey community! I noticed a few minor grammar and phrasing issues in the README.md file (e.g., "2100x over" → "2100x speedup over", "no hand-optimizations" → "no manual optimizations").

I'd like to send a quick PR to improve clarity and flow. Let me know if that's okay!

Thanks,  
Ashwin

