Feature initial submission email

For new submissions, CRAN asks the user to read and agree to its policies; see http://cran.r-project.org/web/packages/policies.html

This patch alters `release`  to ask the user if it is a new submission and if so, asks if they have read and agreed to CRAN policies; adding a sentence stating as much if they do. 

I'm ambivalent as to whether this addition is a good idea. It maybe a good idea to pull up the page with CRAN policies using `browser`.