Encourage best practices for changelogs

Transferring [an issue](https://github.com/INCATools/ontology-development-kit/issues/208) from the ODK:

The OBook should encourage ontology maintainers to follow [those guidelines](https://keepachangelog.com/en/1.0.0/) to maintain their ontology’s changelog – at the very least, there should be a link to those guidelines somewhere.