Add graph for performance benchmark

Author: shg8

README.md

@@ -89,6 +89,10 @@ After installing the [Vulkan SDK](https://www.lunarg.com/vulkan-sdk/), please pr
 
 Please feel free to open an issue if you have any feature suggestions or are interested in contributing.
 
+## Benchmarking
+There is room for performance improvements. See benchmarks on a 4090.
+![cumulative_duration](https://github.com/shg8/3DGS.cpp/assets/38004233/91e6a082-95ec-430d-bbbb-cbb3f63795e0)
+
 ## Contributing
 If you are interested in integrating your Gaussian Splatting variant, please open an issue or a pull request.
 3DGS.cpp's shaders follow the procedures outlined in the original paper, so it should be relatively