• fork and download repository
• install template as a .net core template from nuget
• install template as a .net core template locally

• run dotnet new -i NancyFx.Core.Template::*
• create new project executing dotnet new nancyfx -n PROJECT_NAME -o FOLDER_NAME

• download repository
• run command dotnet new -i PATH*, where PATH is a path to a folder where project is located
• create new project executing dotnet new nancyfx -n PROJECT_NAME -o FOLDER_NAME
• dotnet restore
• dotnet run or dotnet watch run

If you want to extend this template, or create more complex one based on this, don't hold back :)