add Cray PE CDT policy
This is our current CDT policy. Moving it from the classic NERSC page to here.
Understand we will publish the general software policy soon, and we may consider tuning the CDT policy. Before these happen, the CDT policy is the current standing user facing policy. We do not have a "software" menu, I think the CDT policy fits most under the Programming for now. We can move pages around later as needed.