Add changelog file

[lionel-]

I'd love to start tracking progress for stuff like https://github.com/posit-dev/ark/pull/553

One issue is versioning. Because we need to coordinate with Positron, we're currently releasing quite often with a bumped patch version without any release notes.

I think we could keep doing that but start maintaining a changelog for major and minor releases. WDYT @DavisVaughan?

One question is whether we want to track changes made specifically for Positron (e.g. the data viewer comm). I lean towards no? I'm thinking we'd track changes relevant for:

• Jupyter applications (including Positron)
• LSP users (we still aim for an independent LSP and we can pretend it is independent already for changelog purposes)
• Formatter (will be independent from the start)

[DavisVaughan]

I think keeping a running changelog in general is a good idea, and once we get more official about minor/major releases it will become clear which bullet ends up in which section - but for now just a running list of improvements and fixes would go a long way i think

I think I agree regarding what to log