adds zoom and value to examples

doc/torque_api.md

@@ -98,6 +98,12 @@ Map {
   marker-fill-opacity: 0.8;
   marker-fill: #FEE391; 
 }
+#layer[value = 4] { // Use of the value variable, generated by the function specified in -torque-aggregation-function
+  marker-fill: #FABADA; 
+}
+#layer[zoom = 12] { // Use of the zoom variable
+  marker-width: 10;
+}
 ```
 
 ### Data Methods