Enhance README with detailed examples and k-ary comparison table

[carpalsgrabby]

Summary

The README currently contains minimal usage examples. Many users could benefit from seeing actual sample outputs and comparisons between different arities (2, 4, 8, 16).

Proposal

Add to README:

• Example output for a few parameters (e.g., 1M leaves, arity=4).
• A comparison table showing:
  • tree height
  • padding fraction
  • total nodes
• Explanation of how height is computed.
• Provide diagrams / ASCII art for levels.

Benefit

Much better onboarding for developers unfamiliar with k-ary commitment trees.