title: Intellij Community version can not add ruby SDK
body: <p>I want to open a ruby project in Intellij.
  <a href="https://i.stack.imgur.com/tBG0i.png" rel="nofollow noreferrer">Here</a>
  After opened the project. It is not recognized as a ruby project. Because project SDK is not set. My first problem is I can not add ruby sdk into droplist of candidat project SDKs.
   <a href="https://i.stack.imgur.com/zElKy.png" rel="nofollow noreferrer">no place not add ruby sdk into project sdks</a></p>
  
  <p>Does any one have any idea on how to solve this problem ? Thanks </p>