title: UnknownTimeZoneError: 'IST' for apscheduler
body: <p>Iam trying adding a job in apscheduler according to the Indian standard time</p>
  
  <pre><code>scheduler.add_job('cron',start_date=date, hour=time[0], minute=time[1], id=str(job[0]),timezone='IST')
  </code></pre>
  
  <p>But every time its giving an error UnknownTimeZoneError: 'IST'.
  The scheduler is accepting EST,UTC etc. but not IST.</p>
  
  <p>Is IST correct time zone for Indian standard time ? If not how can i schedule a job according to IST ? </p>