Add Optimization paper to index (#40)

* Add Optimization paper

* Update index.md

Co-authored-by: Michael Schlottke-Lakemper <[email protected]>

* Update index.md

Co-authored-by: Michael Schlottke-Lakemper <[email protected]>

---------

Co-authored-by: Michael Schlottke-Lakemper <[email protected]>

Author: DanielDoehring

index.md

@@ -75,6 +75,10 @@ listed above. Author names of Trixi's main developers are in *italics*.
 
 ### 2024
 
+* *Doehring*, *Gassner*, Torrilhon,
+  **Many-Stage Optimal Stabilized Runge-Kutta Methods for Hyperbolic Partial Differential Equations**, 2024.\\
+  [![arXiv:2402.12140](https://img.shields.io/badge/arXiv-2402.12140-yellow)](https://arxiv.org/abs/2402.12140)
+
 * Babbar, Chandrashekar,
   **Lax-Wendroff Flux Reconstruction for advection-diffusion equations with error-based time stepping**, 2024.\\
   [![arXiv:2402.12669](https://img.shields.io/badge/arXiv-2402.12669-yellow)](https://arxiv.org/abs/2402.12669)