title: when install cocoapods get Error?
body: <p>I try and gem install cocoapods I get an error :</p>
  
  <pre><code>ERROR:  While executing gem ... (Gem::FilePermissionError)
      You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
  </code></pre>
  
  <p>what does it mean???</p>