There is no "CHANGES.md" file

I can’t find a description for the format of the file — can you point me towards one?

Looks like it’s supposed to be a Markdown file (https://www.openthefile.net/extension/md). The subversion repository for your project has a readme.md file already, but no changelog.

Well, I am keeping notes of this nature on GitHub:
https://github.com/Digital-Innovation-Lab/prospect/releases

I hope this is sufficient for your purposes. The manual will note any user-level requirements.