title: What's the correct way to add references in .net core -- assembly, or nuget?
body: <p>Issue:
  I'm referencing the IConfiguration interface in a .net core 2.1 library that will run in a linux docker container</p>
  
  <p>Visual Studio 2019 automatically offers to add an assembly reference for me.  If I accept, it references the Microsoft.Extensions.Configuration.Abstractions.dll that is in my program files directory.</p>
  
  <p>However, I see that there is also a nuget packager for this dll online.  </p>
  
  <p>It's easy to say "just trust visual studio", but I've run into issues before with the .net framework where VS (or resharper) will try to add an assembly reference when the assembly it wants to reference is really part of a package that needs to be added.  </p>
  
  <p>I'm a long-timer with .net, just picking up .net core.  What's the correct convention in this case?</p>