Updating #6: Add Geolocator and Google Maps

By adding a few extra lines of JavaScript we can avoid using the `gmaps4rails` gem and especially `underscore.js` which is slightly painful to download and include while it’s really only (visibly) used in one single location anyway.

I’ve also rewritten the JavaScript to be more explicit so coaches may even be able to walk an attendee through it if they chose to do so.

The rest of the instructions have been updated to reflect this change.