+ add loop definition.

res/en/sample.yaml

-title: zendata config syntax
+title: zendata config syntax
 desc: 
 
   # File composition
@@ -43,6 +43,11 @@ desc:
     # select:   If refer to an excel table, you can query a field in it.
     # where:    If refer to an excel table, you can use query conditions.
   
+  # Loop Definition
+  
+    # Define the loop times of a field with a number, e.g. loop:2.
+    # Define the loop times of a field with an interval, e.g. loop:2-10.
+  
   # range definition
 
     # Use commas to connect elements. e.g. range: 1,2,3.