Add arXiv ID to paper citation

Add arXiv:2609.14811 to the plain-text citation in README.md.

README.md

@@ -339,7 +339,7 @@ The paper is available at https://arxiv.org/abs/2609.14811. Cite the paper and t
 ```
 Kareem Khattab, Omar Khattab, and Mohamed Ibrahem.
 Crypto Accounting Bench: Evaluating Frontier and Open-Weight Models on
-Crypto-Asset Accounting Tasks. Entendre Finance, September 2026.
+Crypto-Asset Accounting Tasks. Entendre Finance, September 2026. arXiv:2609.14811.
 ```
 
 ```bibtex