Add CHANGELOG.md

[Jeremy Tuloup]

When updating to newer versions of ypy it's often useful to know about the recent changes.

Some GitHub Releases have a "What's Changed" section which is very useful, but some don't: https://github.com/y-crdt/ypy/releases

Having a CHANGELOG.md file in the repo would make it convenient to have all the changes logged in one place.

[John Waidhofer]

We are aspiring to generate the changelog directly from the commit messages of the PRs. This way GitHub can easily generate the "What's Changed" section from the in the releases tab. Thanks for noting that the logs are a useful resource, and I'll be sure to be more descriptive in future releases, but for now I'd prefer to maintain the current system.

[Jeremy Tuloup]

This way GitHub can easily generate the "What's Changed" section

This is indeed useful, thanks. Although manually clicking on all the GitHub releases when searching for potential changes can be quite tedious.

Of note an initial changelog could be automatically generated with github-activity: https://github.com/executablebooks/github-activity

Using the --all flag:

github-activity executablebooks/github-activity --all

cc @davidbrochart who might be interested in looking into this

[David Brochart]

Thanks @jtpio, I'm wondering if we should use the Jupyter Releaser here, as it's already the case in ypy-websocket?

[Jeremy Tuloup]

I'm wondering if we should use the Jupyter Releaser here

That sounds good 👍

The releaser uses github-activity to generate the changelog.