repo init -u git://github.com/AOKP/platform_manifest.git -b kitkat
for lillipop type like this repo init -u git://github.com/AOKP/platform_manifest.git -b lollipop
Pretty sure this doesn't work yet. To my knowledge, as of writing this AOKP hasn't updated their platform manifests to reflect the changes made by Lollipop. I'm sure they're hard at work, along with the rest of the teams (Cyanogenmod et al) trying to get a release out, so stay tuned for updates. There's going to be a lot of changes happening in the coming weeks.