Consider adding documentation on using CI-Login ssh keys for internal DTN access

[monaghaa]

Without having uploaded an ssh key to CILogon registry, access to the DTNs from within CURC is currently limited to persons who have password-based CLI access (UCB and CSU only).

Adding documentation on how to generate an ssh keypair internally on a CURC node and upload the public part to the CILogon registry would facilitate the following use cases:

• ability to do key-based transfers of data from within batch jobs (since password-based transfers can't be done in batch jobs)
• ability for users with @xsede.org accounts (AMC, Mines, any other RMACC user) to access the DTNs internally, both within or outside of jobs.

This issue requests that CURC consider adding documentation on how to internally access DTNs with ssh keys, if CURC personnel find that the above mentioned use cases are strong enough.