Add upwind and shallow water moment papers (#108)

* add upwind and shallow water moment papers

* update arXiv reference

---------

Co-authored-by: Hendrik Ranocha <ranocha@users.noreply.github.com>

Author: andrewwinters5000

index.md

@@ -116,6 +116,15 @@ listed above. Author names of Trixi.jl's main developers are in *italics*.
 
 ### 2026
 
+* Careage, *Ersing*, Koellermeier, *Winters*,
+  **Entropy analysis and entropy stable DG methods for the shallow water moment equations**, 2026.\\
+  [![arXiv:2602.06513](https://img.shields.io/badge/arXiv-2602.06513-yellow)](https://arxiv.org/abs/2602.06513)
+  [![reproduce me!](https://img.shields.io/badge/reproduce-me!-brightgreen)](https://github.com/patrickersing/paper-2026-swme_dg)
+
+* Mattsson, Niemelä, *Winters*,
+  **Optimal boundary closures for diagonal-norm upwind SBP operators**, 2026.\\
+  [![arXiv:2602.05727](https://img.shields.io/badge/arXiv-2602.05727-yellow)](https://arxiv.org/abs/2602.05727)
+
 * *Ersing*, *Winters*,
   **A new class of entropy stable fluctuations for the discontinuous Galerkin method with application to the Saint-Venant-Exner model**, 2026.\\
   [![arXiv:2601.09450](https://img.shields.io/badge/arXiv-2601.09450-yellow)](https://arxiv.org/abs/2601.09450)