The software side of this project can be pretty tricky, and even scary if you've never jailbroken a phone before, which is required to get the phone to read NFC from the lockscreen.
However, you can still do a lot of fun projects without modding your Android install, just skip that step and head straight to the page about NFC+ Tasker Automation. You won't be able to log into your phone with your nail polish, but you could do all kinds of other things like start playing Barry White when you place your phone on the nightstand (just sayin').