<div class="wojo icon button" data-content="Add users to your feed">
  <i class="icon plus"></i>
</div>

You can assign tooltip to any element using data-content attribute.

Titled

An element can specify tooltip content with a title

<img src="/images/avatars/small/elliot.png" 
data-title="Elliot Fu" 
data-content="Elliot has been a member since July 2015" 
class="wojo avatar image">

<i class="circular heart icon link" 
data-content="Hello. This is a wide pop-up which allows for lots of content with additional space. You can fit a lot of words here and the paragraphs will be pretty wide." 
data-variation="wide"></i>