Release notes

[jholveck]

This is not intended to be merged as a Markdown file. It's just in that form for easier review and discussion for now. Once we've got the content settled, we can reformat this into reStructuredText for the docs.

Based on #471.

Closes #471.

[BoboTiG]

I do not see what can be changed to make it better.

[BoboTiG]

It's now possible to include markdown files in the documentation, that will lower our work with such a PR.
Example: https://github.com/BoboTiG/python-mss/blob/main/docs/source/changelog.rst (and we now have the full project history in the docs: https://python-mss.readthedocs.io/latest/changelog.html)

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Now, I am not sure how to present this file in the documentation, where to put it, under what name? Maybe do you have a clearer idea than me?

At the beginning I wanted to add it under "History" with the title "Next". But maybe this file should be kept for a while (even maybe forever) so it should have its own section 🤔