Add a CHANGELOG.md

[coliff]

Please could you consider adding a CHANGELOG.md so users can see what's change in each release. There is no Changelog tab in the Extension view in VS Code and there have been no 'Releases' made in GitHub so I can't see what was changed between releases.

P.S. Thank you very much for this extension - I find it very helpful.

[lostfictions]

Seconding this! I've unfortunately had several extensions (including official MS ones like microsoft/vscode-eslint) break or change functionality on minor version bumps, so it's very helpful to be able to review what's different.