I think that you may tell for Visual Studio users to extract the content of Steinberg's VST SDK at the location c:\SDKs\vstsdk2.4 because this is the one that is configured in "additional include directories" of the OwlSim project inside Visual Studio solutions.
It's the simplest explanation but you can also create a full tutorial on how to change the "additional include directories" of the OwlSim project :-)
I think that you may tell for Visual Studio users to extract the content of Steinberg's VST SDK at the location c:\SDKs\vstsdk2.4 because this is the one that is configured in "additional include directories" of the OwlSim project inside Visual Studio solutions.
It's the simplest explanation but you can also create a full tutorial on how to change the "additional include directories" of the OwlSim project :-)