Update README with improved docs

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Summary

• Adds hyperlinks to TP-7 and Octatrack MKII product pages in the intro
• Rewrites the intro paragraph to include BPM analysis and Octatrack padding features
• Reorganises usage section with dedicated subsections for Analyze, Sync, and Sets (experimental)
• Removes redundant set editor keyboard shortcut table and sample rate selection section (content folded into prose)
• Cleans up brew install instructions and other minor wording improvements

Test plan

• Review README renders correctly on GitHub