title: why does yarn warn when adding a dependency to the root workspaces package.json
body: <p>Whenever I add a dependency to the root of the workspaces project:</p>
  
  <p>e.g.</p>
  
  <p><code>yarn add assets-webpack-plugin -D</code></p>
  
  <p>I get the following error:</p>
  
  <blockquote>
    <p>Running this command will add the dependency to the workspace root rather than the workspace itself, which might not be what you want - if you really meant it, make it explicit by running this command again with the -W flag (or --ignore-workspace-root-check).</p>
  </blockquote>
  
  <p>The alternative is to add it to every project that needs it and then it will you have the problem of each project having different dependencies and lock files.</p>