Update README and documentation

The README should be updated to give some examples for using the new functions that we've added since the last time we updated the README.

Also, we've got this hanging discussion from an MR that was just merged:

David: "The word Diff in the function name is throwing me a bit. What does it stand for? Best I can tell we're just verifying that a set of ranges are part of a Merkle root, that's not really a diff.

Guess we're stuck with it now but we should probably talk about the name at the top of the file."

Chris: "I always thought it refers to the fact that the proof is used to show the difference between an old and a new set of roots.

What do you mean by "talk about the name"? We could change it or leave it like that but a comment is probably something we are never going to come back to. Like many comments we have deleted in the past because they are outdated. If it warrants an issue we can do that instead to make sure we are always aware of it."

David: "But it doesn't show the difference between an old and new set of roots, it only shows you ranges of data that are inside the current root. If you make changes you have to compute the diff yourself."