Document fully-qualified library ref in "Pulling a Container"

[EmmEff]

Which Document page:

"Pulling a Container" (https://sylabs.io/guides/3.7/user-guide/cloud_library.html#pulling-a-container for 3.7)

Expected results:

What are you expecting to see?

Add documentation describing how to use a fully-qualified library reference containing host name:

library://<hostname>/<entity>/<collection>/<container>/<image>[:tag]

• Host name must be that of the cloud library (ie. library.DOMAIN)
• Library refs containing a host name must be fully-qualified (entity/collection/container[:tag])
• Specifying a host name does not override system exclusive settings
• Pulls from library ref containing host name are unauthenticated

Actual results:

What is the problem, what's misspelled, or what's missing?

This is a new feature so documentation did not exist previously