Hi there - you don't even need a plugin to do that. :-)
If you have the HTML code for your badge, just head to Appearance > Widgets, drag a text widget over to one of your four footer widget areas, and copy-paste your code into the text widget box. Here's a step by step guide:
If you haven't been given the code, you can manually add the code yourself. A simple way to do that is by creating a draft post, and uploading your badge and adding a link using the Visual Editor. Once you're done, Click the Text/HTML tab, and copy out the code that's been generated, so you can paste it into your text widget.
Let me know how it goes!