Add a CHANGELOG

[hadronized]

I’m not sure it’s as easy as it seems, as one must either:

• Go through the git log history to re-create the changelog by hand… might be time-exhausting.
• Or just pin the current version as the “first version in the CHANGELOG” and just keep the document updated for future releases.

[bvssvni]

The second option is better than nothing, and the first option can be done later.