Memoset documentation

[porcuquine]

While this module documentation is useful to document the building blocks, I would love to see some use-case level doc: what can I find in this module, what can I use it for, and what can I not use it for?

The core piece of information that we may want to volunteer at the top-level, is that this particular coprocessor takes assumptions about Lurk data structures (and their hash-consing), because it is meant to represent Lurk evaluation proofs. That's not a thing that all coprocessors do (e.g sha256) and laying that out in a couple sentences at the top should help the reader interpret the meaning of a struct named "Transcript" at the top of the file (i.e. this is not a garden-variety RO).

Originally posted by @huitseeker in https://github.com/lurk-lab/lurk-rs/pull/1004#discussion_r1449281987