fix docs links

docs/extraction-and-validation.md

@@ -31,16 +31,24 @@ For instance, if we want to get `Content-Type` in response headers, then we can
 There might be slight difference on list, cos we can use index to locate list item. For example, `Guangzhou` in response content can be specified by `content.person.cities.0`.
 
 ```text
-{"resp_status_code": "status_code"},
-{"resp_headers_content_type": "headers.content-type"},
-{"resp_content_body_success": "body.success"},
-{"resp_content_content_success": "content.success"},
-{"resp_content_text_success": "text.success"},
-{"resp_content_person_first_name": "content.person.name.first_name"},
-{"resp_content_cities_1": "content.person.cities.1"}
+# get status code
+status_code
+
+# get headers field
+headers.content-type
+
+# get content field
+body.success
+content.success
+text.success
+content.person.name.first_name
+content.person.cities.1
 ```
 
 ```yaml
+extract_binds:
+    - content_type: headers.content-type
+    - first_name: content.person.name.first_name
 validators:
     - {"check": "status_code", "comparator": "eq", "expected": 200}
     - {"check": "headers.content-type", "expected": "application/json"}