Add CHANGELOG.md file

[khanguslee]

This package has seen a lot of updates in the past year (amazing!), but it would be great if we could create a CHANGELOG.md file to keep track of what has changed between each version.

Luckily, each update has been fairly small so figuring out what is a breaking change has been fairly simple to follow along. I just want to standardise this procedure so that consumers of this package can update this dependency knowing any risks and/or features added.