Docs: note where library defaults diverge from the arXiv 2607.20548 recipe (momentum, weight decay, NS iterations, RMS scale)

The recent paper "SOAP, Muon, and Beyond" (arXiv 2607.20548) points readers to this repository as its released code. Readers who install the library and use Muon's constructor defaults get a materially different optimizer than the paper's experiments on four axes:

Since the paper itself argues optimizer comparisons are uninterpretable without matched update RMS, a short README note or a checked-in "paper recipe" reference config would prevent exactly the silent config mismatch the paper warns about. The only current breadcrumb is the extra_scale_factor docstring's optional 0.2 mention, which cites arXiv 2502.16982 rather than the recipe. Happy to PR the table above into the README if that's welcome.

Start by comparing the Muon constructor defaults in muon.py with the proposed table and the existing extra_scale_factor docstring. Review the README structure and the cited paper context, then add a concise note or checked-in paper recipe reference covering the four divergences and their sources. Done means readers can identify the paper settings separately from the library defaults.