I'm also going to make a new official Installer type build in nearish future. I've been and still am postponing it so more datafile (ruleset/tileset/etc) format changes go in before -> less after the build.
Ruleset update instructions to current S2_6 development revision: http://freeciv.wikia.com/wiki/How_to_update_a_ruleset_from_2.5_to_2.6
Ticket about the datafileformatfreeze (dfff) task: Task #7814
Various topics about the game, the website, or anything else Freeciv related that doesn't fit elsewhere.