title: Post message via slack api with file attachment
body: <p>I am trying to use Python SDK to post a file to Slack.
  However, I am also trying to mention some people with <code>@</code> in the uploaded message.</p>
  
  <p>I am trying this code:</p>
  
  <pre><code>import os
  import slack
  client = slack.WebClient(token='xoxp-asksjdfj')
  res = client.files_upload(channels='#uploads', file='a.txt', title='@john')
  </code></pre>
  
  <p>However, the title doesn't show up as a mention.  Is there a way to do that ?
  Thanks</p>