add other plot

Author: SimonBlanke

README.md

@@ -50,7 +50,7 @@ Test functions for benchmarking optimization algorithms in Python.
 ---
 
 <a href="surface plot">
-  <img src="./docs/source/_static/rastrigin_surface.svg" width="240" align="right" alt="Bayesian Optimization on Ackley Function">
+  <img src="./docs/source/_static/drop_wave_surface.svg" width="240" align="right" alt="Bayesian Optimization on Ackley Function">
 </a>
 
 **Surfaces** is a Python library providing standardized test functions for evaluating and comparing optimization algorithms. It includes algebraic benchmark functions from optimization literature, machine learning hyperparameter optimization problems, and constrained engineering design problems.