Fixed linker errors of imgui backend on windows

examples/main.cpp

@@ -7,6 +7,11 @@
 #include "Host/GraphicsAppManager.hpp"
 #include "ExampleApps/CubesExampleApp.hpp"
 
+// NOTE(vb): I couldn't find a way of linking with imgui_glfw using CMake
+#ifdef _WIN32
+# include "backends/imgui_impl_glfw.cpp"
+#endif
+
 using namespace OpenVulkano;
 
 int main(int argc, char** argv)