Updated 教师偏好设置接口 (markdown)

 #### 接口地址
 
-  >     /teacher/preference/setting
+  >     /teacher/preference
 
 ####请求方式
 
@@ -17,7 +17,7 @@
 ######设置成功
 
 ```json
-
+状态码：200
 {
   "relation_material": "人教2012版-七上",
   "difficulties": [
@@ -27,25 +27,26 @@
   ],
   "fit_grade": "初一"
 }
+
 ```
 ######设置失败情况1
 
 ```json
-
+状态码：400
   "preference_setting_failed": "难度未选择"
 
 ```
 ######设置失败情况2
 
 ```json
-
+状态码：400
   "preference_setting_failed": "适合年级未选择"
 
 ```
 ######设置失败情况3
 
 ```json
-
+状态码：500
   "preference_setting_failed": "其他异常"
 
 ```