That information itself comes from outside Hugo, but you could either make it available to Hugo at or before deploy time, or, do it dynamically. As @maiki mentioned sources might be your server log, Google Analytics, or, you could use a service like http://www.reliablecounter.com/. I’m not vouching for that, but, you could try it or search for others like it.
If your web server has stats like awstats or webalyzer (which just looks at your server logs, but, presents in a useful way) you might be able to somehow extract that info into some useful format that Hugo can use, i.e. putting it into a data file in json which you parse and display when you build. Similarly, you could use Google Analytic’s API via some script, to pull its data for your site into a json for Hugo parsing.