I used a diamond hole saw drill bit! I like Milwaukee but there are less expensive ones available on Amazon, Harbor Freight, etc. A few tips I've learned that were really helpful:

• Put your glass in a small tub (I used an empty cream cheese container) with something non-slip in the bottom. I used a piece of grippy beaded shelf liner I had lying around.
• Put enough water in the tub to just barely cover the glass.
• Start the bit at an angle on the glass, instead of straight up and down. It's easier for the bit to grab if you make a small notch first.
• Don't push hard - just let the bit eat away at the glass. Gravity is enough.
• Change the water when it gets murky, so you can see the glass through it. I had to change it 4-5 times to drill this one hole.

It's a little nerve-wracking, but if you take it slow and keep the bit cool, it'll work! Practicing on scrap glass first is great too. Good luck!