Add a Top Bar, you can link in the Top bar to any page you like, your getting started or directly to the WA signup page. The advantage of a top bar is that it doesn't interfere with your content, like a pop-up does.

The plugin I used for the Top bar is "WPFront Notification Bar" by Siam Mohan. You can adjust the colors, the font and write a text of your own choice.

My theme has a side wide footer widget area, and there you can add your own advertisement. When your theme doesn't have this footer widget, you can make use of a plugin called "Header and Footer scripts" by Digital Libaration to be able to advertise your own stuff in your footer.

Create your own ads in between your content. The way like Google AdSense does. You can do that too. But you are linking to your own Getting Started page.