chore(docs): Binary Documentation

[refcell]

Description

Following the precedent set in reth, minimal binary documentation should be done inline with extensive markdown book docs to avoid duplicate, and out-of-sync documentation.

For this issue, the opup binary readme.md file should be removed and minimal inline docs should be added to opup/src/lib.rs.

In the future, more extensive documentation will be added to documents in the docs/ mdbook.