📝 Documentation: add CHANGELOGs for each package

### Bug Report Checklist - [x] I have pulled the latest `main` branch of the repository. - [x] I have [searched for related issues](https://github.com/JoshuaKGoldberg/sentences-per-line/issues?q=is%3Aissue) and found none that matched my issue. ### Overview The new multi-package structure doesn't include CHANGELOG's for each package. ### Additional Info _No response_