Update README to reflect 2.0 default testing

Added some details to the addition of `distutil` tests introduced in 2.0.  Since we have scripted testing, it seems useful for users to make sure their installation is working.

@seancribbs See if this is reasonable or not. I'm happy to revise in any direction you see fit.
True.  But currently our tests go against a single node.  I know you are working on a testing cluster for SC.  I guess I could change it to "node" for now for current correctness.