Show a changelog to user after (major) updates

[tcrammond]

It would be good to prompt the user to look at a changelog after a major update. This is also an opportunity to improve the changelog - including relevant screenshots, for example.

Perhaps highlighting the settings button in the toolbar popup, and showing the latest changelog in the setting view.

Prime example is making a significant change, such as introducing permissions to Firefox which happened in the latest release. Or changing the way an integration works.

It's an extra opportunity to:

• Educate users about changes that directly affect their usage of the extension
• increase engagement with new features we add
• Perhaps avoid the need to contact support if something significant changes and causes friction

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onInstalled

[germn]

If you're going to do it, please add ability to disable such notification.