First, build gadget.xml by running the following.
make
Next, host gadget.xml somewhere publicly accessible. Say, at the URL
<gadgeturl>. Then, go to the following URL in your browser.
http://www.google.com/calendar/render?gadgeturl=<gadgeturl>
Note that Google caches the gadget for up to an hour. So if you want to refresh it sooner than that, add a "cache-busting" URL query string parameter.
You may need to add https://www.google.com to the list of authorized
JavaScript origins in your browser.