improved documentation for the idField table option (#4233)

* improved documentation for the idField table option

* Update table-options.md

site/docs/api/table-options.md

@@ -1005,7 +1005,7 @@ The table options are defined in `jQuery.fn.bootstrapTable.defaults`.
 
 - **Detail:**
 
-  Indicate which field is an identity field.
+  Indicate which field will be used as checkbox/radiobox value, its the counterpart to [selectItemName](https://bootstrap-table.com/docs/api/table-options/#selectitemname).
 
 - **Default:** `undefined`