title: Is there a way to get Sonar to verify that a file exists?
body: <p>Something which is a consistent problem in projects I've been working on is a lack of a README (of any form). I'd like to have Sonar verify that either a README file exists in a project root or that a <code>docs/</code> folder exists which has at least one file in it.</p>
  
  <p>I haven't seen these options as a Sonar rule.</p>
  
  <p>I am more than willing to write an extension (I have before for other custom rules), but it seems like I would have to have the same check called for every file in the project instead of just once on the project root.</p>
  
  <p>Is there an existing rule to check for a certain file/folder?
  If not, is there a way to write an extension to only check for that file/folder once?</p>