title: Can't find "rackup" command?
body: <p><a href="http://titusd.co.uk/2010/04/07/a-beginners-sinatra-tutorial" rel="nofollow">http://titusd.co.uk/2010/04/07/a-beginners-sinatra-tutorial</a></p>
  
  <p>I was trying to run <code>rackup config.ru</code> from the command line as instructed in the tutorial above in section 4. It ended up saying "No command 'rackup' found". </p>
  
  <p>Any idea what happened?</p>