title: Cannot add appsettings.json inside WPF project .net core 3.0
body: <p>I am creating a WPF project using .net Core 3.0, and I am having trouble adding the item  <code>appsettings.json</code> file to my project which is to be used to store my DB connection string.</p>
  <p>I would normally have done inside the <code>app.config</code>, but this has now been removed from .net Core.</p>
  <p>Everywhere mentions using <code>appsettings.json</code> as a replacement, and that it has to be maunally added &amp; initialised in the <code>OnStartUp()</code> function using an instance of <code>IConfiguration</code>, and there after using Dependency Injection to pass in the config class into the project.</p>
  <p>But my issue is that can only add the <code>appsettings.json</code> item on  asp.net Core projects? not my WPF solution.</p>
  <p>I do apologies if I'm missing something very obvious (which I probably am), I just can't seem to find any solutions.</p>