Updated 教师偏好设置接口 (markdown)

@@ -6,11 +6,11 @@
 
   >     POST请求 
 
-####参数格式
-
+####参数格式  
   >     - "fit_grade":"初一"
-  >     - "difficulty":"1"
+  >     - "difficulties":"1","2"
   >     - "relation_material":"人教2012版-七上"
+  >     其中fit_grade，relation_material是单选，difficulties为多选
 
 ####返回值
 
@@ -18,14 +18,14 @@
 
    ```json
   {
-   "偏好设置": "success"
+   "preference_setting": "success"
   }
 ```
 ######设置失败
 
 ```json
   {
-   "偏好设置": "failed"
+   "preference_setting": "failed"
   }
 ```