Restore 0.5.0 migrations and explain the removal of the very old ones

Author: r41d

README.md

@@ -22,6 +22,7 @@ GNU GPLv3
 - Redo some (well, most...) of the graphics
 - Many adaptions in data model
 - Make double-electric-furnace research more expensive
+- Remove very old migrations because the last update was 3 years ago and we had to change so much for Factorio 2.0, that I now consider these even older migrations unnecessary baggage
 
 ## 0.5.1
 - Fix migrations

migrations/DoubleFurnace_0.5.0.json

@@ -0,0 +1,7 @@
+{
+  "technology":
+  [
+    [ "double-smelting-tech", "double-smelting-tech-electric" ]
+  ]
+}
+

migrations/DoubleFurnace_0.5.0.lua

@@ -0,0 +1,8 @@
+-- Unlock the steel double furnace technology if double-smelting-tech is already researched
+for i, force in pairs(game.forces) do
+  if force.technologies["double-smelting-tech-electric"].researched then
+    -- setting the technology to researched should also enable the recipe
+    force.technologies["double-smelting-tech-steel"].researched = true
+  end
+end
+