Write down how to cut a release

Six months from now none of this will be obvious: which of the two version
numbers has to go up, that the changelog file is named after the
versionCode rather than the version name, and that the tag has to keep its
v prefix — checkupdates takes the tag name verbatim as the commit to
build, so a tag named 1.1 would quietly break the automation.

Also records the two things that make the screenshots reproducible, both
of which cost time to find: a headless capture lands whenever the
virtual-time budget runs out rather than when the script finishes, and
CSS transitions don't advance under it, so a panel caught mid-transition
photographs in its old colour.

States the part that is easy to get wrong in the other direction too:
after the first submission there is nothing to do in fdroiddata. The bot
watches the tags here.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -6,6 +6,10 @@ Backgammon Galaxy control. Defaults to 3:00 + 12s.
 
 Plain HTML, CSS and JavaScript. No frameworks, no fonts, no images, no network.
 
+There's an Android package too, in `android/` — a WebView around the same
+`public_html/`, so the two can't drift. It declares no permissions at all. See
+[RELEASING.md](RELEASING.md) for how to cut a new version for F-Droid.
+
 ## Getting it onto your phone
 
 Chrome will only offer a real install over HTTPS, so the file needs a host.