Beep boop add f-droid (#1087)

Full credit to @ZacBytes for the initial implementation.

core/assets/bundles/bundle.properties

@@ -10,6 +10,7 @@ link.dev-builds.description = Unstable development builds
 link.trello.description = Official Trello board for planned features
 link.itch.io.description = itch.io page with PC downloads
 link.google-play.description = Google Play store listing
+link.f-droid.description = F-Droid catalogue listing
 link.wiki.description = Official Mindustry wiki
 linkfail = Failed to open link!\nThe URL has been copied to your clipboard.
 screenshot = Screenshot saved to {0}