Update readme for stonecutter

mods/ITEMS/mcl_stonecutter/README.md

@@ -2,6 +2,15 @@ mcl_stonecutter
 ===============
 Adds the stonecutter block. Used to cut stone like materials into stairs, slabs, etc. Also used as the Stone Mason Villager's jobsite.
 
+### Adding recipes
+
+* To add a new compatible input the item needs to be in the group "stonecuttable".
+* It's output item needs to be in the group "stonecutter_output".
+* "stonecuttable" and "stonecutter_output" need to have the same number.
+* Items like polished granite should only be able to make it's polished variants
+while normal granite can make both. These inputs and outputs need to be in the group 
+ "stonecutter_stage".
+
 License of code
 ---------------
 See the main MineClone 2 README.md file.