It's really two steps, one to initiate the installation and then to approve it ("yes").

You can wrap the initiation any way you like. I prefer to make it resemble an app store people are familiar with. Screen shots, user feedback, a description with a "download" button. This communicates the intention pretty well even though it adds an extra step to the process.

I find the biggest hurdle is that people don't realize they can install an "app" so easily and so I try to bridge the knowledge gap.