Update screenshots

[helen]

Is your enhancement related to a problem? Please describe.

The current screenshot is now slightly outdated because of the addition of the revisions link.

Describe the solution you'd like

I'd like to update the current screenshot (contents can be found in CONTRIBUTING.md) and also add screenshots of the revisions screen and the new notice that shows if you have an ads.txt file on the server. These should be at HiDPI (Retina).

Designs
See current

Describe alternatives you've considered
n/a

Additional context
This can be done independently of a milestone - if other PRs are merged before this is handled, I suggest making a PR against master instead of develop, then once that PR is merged, allow the readme/asset updater Action to run before merging master back into develop.