title: (when adding jar) - Module "android" must not contain source root
body: <p>I'm trying to add gdx-tools.jar to a libGDX project in IntelliJ. The result:</p>
  
  <blockquote>
    <p>Module "android" must not contain source root ".../android/src". The
    root already belongs to module "android".</p>
  </blockquote>
  
  <p>This is what I've tried:</p>
  
  <p>project structure > libraries > new project library > java > select "gdx-tools.jar" >select module "desktop"</p>
  
  <p>project structure > modules > select "desktop" > new > jars or directories > select "gdx-tools.jar" > </p>
  
  <p>Ideas?</p>