Keep a changelog for CLI

[renestalder]

CLI 0.17.0 was recently released. The changelog files in the root or the CLI folder weren't updated in years. The release page on GitHub doesn't document the CLI changes. We have to compare over 80 commits in source.

We would love to have a changelog that summarizes the most important changes, especially assuming minor bumps in pre 1.0 versions are considered «breaking changes» in SemVer. So we are able to make better predictions about what an update is doing.