adding release and publish instructions

@arschles I think we need to update the release steps so publish-signed happens as part of the release steps defined here: https://github.com/paypal/cascade/blob/develop/project/Build.scala#L54. We want things to publish correctly as well when you run ```release cross with-defaults```. Take a look at Newman: https://github.com/stackmob/newman/blob/develop/build.sbt#L70.