Add changelog.md

[mapl]

Please add a changelog.md to communicate changes

[nol166]

it would be cool to do something like this: https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/CHANGELOG.md

[zanhk]

liKe ThIs
https://www.epicgames.com/fortnite/en-US/news/category/patch%20notes

[nhooyr]

We will definitely do this for future releases.

[AckerApple]

Looking for that changelog. Found this issue instead, was going to create an issue.

I was on 3.5.0 and now on 3.8.0 and want to learn whats updated

[code-asher]

For the time being we put all the changes in the GitHub releases which can be viewed here: https://github.com/cdr/code-server/releases