Make V8 releases script add useful links.

BUG=
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/227303005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20713 ce2b1a6d-e550-0410-aec6-3dcde31c8c00