Could you update the CHANGELOG for 2.8.3? https://github.com/piwik/piwik/blob/master/CHANGELOG.md It would be nice to have it in the release archive too.
Please consider writing a relese script that does every step (or notifies you what should be done manually).
This document is the "changelog for Piwik platform developers". If I'm not mistaken, if there is nothing for a specific version, that means that nothing has changed for platform developers.
Is that the changelog you are interested into? Or is it http://piwik.org/changelog/?
No worries :)