title: how to set label for bar stack to echarts
body: <p>I am using echarts.
  this is my chart:</p>
  
  <p><a href="https://i.stack.imgur.com/uEvKi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uEvKi.png" alt="echarts"></a></p>
  
  <p>I have several xaxix this picture shows one xaxis data and two bar(stack).
  info:stack put data on top of each other in one xaxis data.
  so in this case I have Two bar</p>
  
  <p>my question is: how can I set label for each stack(not xaxis label I am showing with red) there is an option for this purpose?</p>