Go for it! Have it just after you've fed the baby and enjoy it. Alcohol does reach the breastmilk in the same quantities as blood so the baby will get a bit, but one glass will be a tiny amount.
The biggest danger of drinking with a newborn is that you can't care for the baby, but that would have to be quite a bit of drink!
If you've not drunk for a while then I'd advise you to only have a small glass and see how you get on. It might just make you really, really sleepy and if you're co-sleeping this could be a problem.