If you are finished with your button, upload it somewhere else and get the url or the direct link of your button..
In an HTML widget just copy the following and change the necessary informations
Your URL or the address of your site.
Your badge url it is where your image is located
The first code is actually just your button and the location it will direct when clicked. Of course when you asked people to grab your button and display it in their site, you will have to show them what they are grabbing.