Add PicoSHA2 note to README.md and other places
Using this code requires acknowledgement.
I used the code to compute the SHA256 hash used as the key for stuff in the store. Using SHA256 means teh store can be moved to S3 and will have good parallel performance - and we need something unique. We could use an id passed/returned by CMR. Should be easy enough to make that change.
Using SHA256 will mean we need to maintain some sort of inventory (or go nuts looking for stuff in said store because the hashes are 100% opaque).