title: how do I use first letters of my UITableview Sections and not the entire section label?
body: <p>So I'm using the below code to get the index listed for my table view...however it is return the entire section header which is not really what I want. I want to be able to return just a first letter to let people get quickly to the section of the table I need. I'm not sure how to implement this. </p>
  
  <p>Thanks</p>
  
  <p><a href="https://i.stack.imgur.com/ubZvU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ubZvU.png" alt="Index is using full names.."></a></p>
  
  <pre><code>func sectionIndexTitles(for tableView: UITableView) -&gt; [String]? {
      return keys
  }
  </code></pre>