The essence of git is to track the files rather than the folders. Hence, if you just want to track the empty folder, which basically can not be supported in git and on github.
The solution is to add a .gitkeep file to the folder.
Due to the property of hidden file, the file usually does not show up. And you can track it in the git, with the configuration in .gitignore:
targetFolder/*
!targetFolder/.gitkeep
You can just leave it as the blank file, or you can add some explanation in the file.