Update README.md

README.md

@@ -3,6 +3,7 @@ A three-variate turbulent wind field (u,v and w components) is simulated in thre
 
 [![View Wind field simulation (the fast version) on File Exchange](https://www.mathworks.com/matlabcentral/images/matlab-file-exchange.svg)](https://se.mathworks.com/matlabcentral/fileexchange/68632-wind-field-simulation-the-fast-version)
 [![DOI](https://zenodo.org/badge/248844343.svg)](https://zenodo.org/badge/latestdoi/248844343)
+[![Donation](https://camo.githubusercontent.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)](https://www.buymeacoffee.com/echeynet)
 
 ## Summary
 A turbulent wind field (u,v,w, components) in 3-D (two dimensions for space and one for the time) is simulated using random processes.  The computational efficiency of the simulation relies on Ref. [1], which leads to a significantly shorter simulation time than the function windSim, also available on fileExchange. However,  only the case of a regular 2D vertical grid normal to the flow is here considered.