new tutorial example

doc/tutorial/MorefoodEng.gf

@@ -0,0 +1,7 @@
+concrete MorefoodEng of Morefood = FoodEng ** {
+    lincat
+      Question = {s : Str} ;
+    lin
+      QIs item quality = {s = "is" ++ item.s ++ quality.s} ;
+      Pizza = {s = "pizza"} ;
+}