Add "What has changed?" page

[bartlomieju]

It would be great if manual had "What has changed?" page. It's not easy right now for users to see what new additions where made to manual since the last release.

It's unreasonable to expect users to go to Github repository and see commit log to figure this out. This could be somehow generated using git log and then mapped to actual manual pages with additions.

CC @lucacasonato

[kwhinnery]

still a good idea

[hashrock]

We need to cut the release version, but is GitHub's auto generated release note sufficient?
Another option is a conventional changelog, but forcing a commit message doesn't seem to fit with the documentation website.

[thisisjofrank]

@bartlomieju is this still something we're missing? Or is it now covered by release blog posts?