Update Readme and Sample hocon for new settings

We don't have documentation around how to use `BackwardsCompatibleSurrogatedFormatter`, let alone in a way useful to users (If they REALLY want to for some reason, they'll probably have to override a serializerID or similar.

Also we should provide some docs and explanation around:

- LZ4 Settings
- `converters` vs `converters-override`
- May be worth providing an example of how to 'override' TypelessFormatter while safely respecting Akka surrogates, etc.

Start with the repository README and sample HOCON configuration mentioned in the issue, then inspect the existing serialization settings documentation. Done means documenting BackwardsCompatibleSurrogatedFormatter, LZ4 settings, the difference between converters and converters-override, and a safe TypelessFormatter override example that respects Akka surrogates.

Written by the indexing model from the issue text.