The browser won't let you access the user's location without them clicking an acceptance dialog, and you may not want such a dialog to appear when the page first loads because they may well dismiss that dialog until they have read the page content (that's certainly what I would do).
Once the user has denied permission to access the location it's very difficult for you to get past that, you can't ask again (you have to educate them about how to update the browser settings so that you can use the location).
So, my advice would be: don't do it.
But if you really want to, then the easiest way would be to use the DOM ready event to trigger a single line of jQuery which fires the click event on the "Use my location" button (check in the browser dev tools to see the best way to target the button for selection).