title: Flake8 in VS Code: unused imports not underlined
body: <p>I've installed Flake8 using Anaconda prompt, to an environment I'm using. I'm using VS Code.</p>
  
  <p>I recently used the terminal in VS Code to tell Flake8 to ignore certain errors and I think one of them was F401, which concerns unused imports. </p>
  
  <p>It's very clear how to ignore a given error, but I can't find anything about how to "unignore" it.</p>
  
  <p>I know Flake8 is working in my environment because other errors are given squiggly underlines in VS Code.</p>
  
  <p><strong>How can I make the squiggly underlines reappear for F401?</strong></p>
  
  <p>NB. I'm unable to locate the config file discussed in the Flake8 documentation. If I could do so, I imagine I'd just be able to delete the line about ignoring F401. I couldn't find out how to locate the config file that's being applied when I call flake8 from VS Code. (As far as I can tell the documentation only tells you how to create a overriding config file.)</p>