docs: Real screenshots

Replace the placeholder-content screenshots with a demo instance that
serves real CC-licensed open movies (Blender Foundation, framatube),
so the app looks like what it is: a video player with real thumbnails,
real durations and real playback.

README.md

@@ -16,8 +16,10 @@ all, privacy levels included.
 
 ## What it looks like
 
-Screenshots were taken against a demo instance with placeholder content, on an
-emulator. The app itself is on a dark theme, made for a 10-foot couch view.
+Screenshots come from a demo instance serving real, CC-licensed open-movie
+content, courtesy of the [Blender Foundation](https://www.blender.org/) movies
+and the [A propos de PeerTube](https://framatube.org) channel. All of it plays
+in the app.
 
 The home screen. Continue watching picks up at the position the server saved,
 new videos first, page after page.