add intersection upgrade

docs/js/upgrade.js

@@ -4,6 +4,10 @@ exec.doNothing = function() {
 
 }
 
+exec.intersectThings = function() {
+
+}
+
 exec.addCube = function () {
     cubePos.push([Math.random() * 1000 - 500, Math.random() * 1000 - 500, Math.random() * 30 - 200,
     Math.random() * 2 - 1, Math.random() * 2 - 1, Math.random() * 2 - 1
@@ -21,6 +25,12 @@ upgrades = [
         'price': 1000,
         'exec': 'doNothing',
         'desc': 'Earlier-bought Sets are more powerful'
+    },
+    {
+        'name': 'Intersection',
+        'price': 1000,
+        'exec': 'intersectThings',
+        'desc': 'Sets become easier to click'
     }
 ];