Changelog improvement

[xsuchy]

I already contributed several PR. Part of the contribution is documenting the change in CHANGELOG.rst. But every time a PR that touches this file it will introduce conflict in other PRs that are waiting for review.
And rebasing the PR is painful.

In several projects, I have already used Towncrier https://towncrier.readthedocs.io/ to track changelog changes. Every PR creates a separate file in a specific directory, and during a release, you run towncrier build ... and these fragments are merged into the Changelog. Here is an example https://towncrier.readthedocs.io/en/stable/tutorial.html#creating-news-fragments

The benefits are that there are no conflicts when merging PR, and contributors are more likely to contribute the documentation.