Web and .NET Core side-by-side projects

I am still pretty early-on with Rider so maybe I am missing something obvious. But I started a .NET Core Web API project to act as my back-end and then I wanted to add an Angular 6 folder at the same level as my .NET Core folder. I assumed it would work similar to WebStorm since I know WS is somewhat built-in to the other Jetbrains IDEs. I wanted to add it as existing source since I created with the CLI, but it seems Rider don't add anything that doesn't have a .NET Core solution file.

Am I doing this wrong? How do I get a non-.NET Core client-side project folder side-by-side with my .NET Core folder where they could both be edited within Rider? I could put the client-side code inside the .NET Core folder but I don't really want to do that. Is Rider not really considered to have WebStorm built-in? Thank you!