Update README

sample/vars/test-subtree.json

@@ -1,28 +1,37 @@
 {
-  "version": "1.8.1",
-  "name": "test-subtree",
+  "$override": {
+  },
+  "custom": {
+  },
   "desc": "",
-  "firstid": 1,
   "export": true,
-  "group": [],
-  "import": ["vars/declare-core.json"],
-  "vars": [
-    {
-      "name": "test",
-      "desc": "测试"
-    }
+  "group": [
   ],
+  "import": [
+    "vars/declare-core.json"
+  ],
+  "name": "test-subtree",
+  "prefix": "",
   "root": {
-    "id": "1",
-    "name": "Sequence",
+    "$id": "8kjkfpkMB7",
     "children": [
       {
-        "id": "2",
-        "name": "Log",
+        "$id": "3yauu6FM1P",
         "args": {
           "message": "hello"
-        }
+        },
+        "id": "2",
+        "name": "Log"
       }
-    ]
-  }
-}
+    ],
+    "id": "1",
+    "name": "Sequence"
+  },
+  "vars": [
+    {
+      "desc": "测试",
+      "name": "test"
+    }
+  ],
+  "version": "2.0.0"
+}