I have one. 
It’s in my project, it’s more of an issue of “How to correctly use it.” There’s not much documentation on the functions that are available for use in that context. For example, in openGL Documentation (un-related), it says something along the lines of “A Fragment Shader must at a minimum write to gl_FragColor.” That’s awesome! What’s the Build.cs file supposed to do? At a minimum? Or maximum? Lol. That’s what’s confusing. To me… It’s just there. Obviously for something but for what? 
And how do I use it properly.