Move basic example to README and Literate Haskell

Not sure, what will be the best approach for this: relative path in the `trial-example` executable stanza or a new top-level project.

Start by locating the current basic example and the `trial-example` executable stanza, then read the project README and existing Literate Haskell material. Clarify whether the example belongs in the README, Literate Haskell, or a new top-level project, and consider the relative-path implications. Done means the example has a documented, maintainable home and the executable arrangement is resolved.

Written by the indexing model from the issue text.