I finally found an anchor for how to write a README. The README should supply progressively enhancing explanations.
After reading the first sentence, you know whether this thing is in the ballpark of something you’re interested in. The first paragraph narrows that understanding, now you can give a clearer yes/no answer. If yes, what follows should specialize the value proposition into something you can use. Dependency coordinates and a small example.
Whereas the beginning of a REAME must briefly explain the core idea, the rest can afford more content. Structure headings by reader interest, and they may do the progressive explanation enhancement on their own. Does this heading matter to me? Yes/no? Read or not read. There is no try.