[doc] add usage

Author: ronething

README.md

@@ -3,14 +3,21 @@
 **Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*
 
 - [leetcode-question-today](#leetcode-question-today)
+  - [usage](#usage)
   - [效果图](#%E6%95%88%E6%9E%9C%E5%9B%BE)
   - [acknowledgement](#acknowledgement)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
 ## leetcode-question-today
 
-leetcode 每日一题推送
+leetcode 每日一题推送(目前支持 slack/wecom)
+
+### usage
+
+1、fork this repo
+2、添加 secret, SLACK_URL 为对应的 token 即可
+3、可自行拓展其他的通知方式
 
 ### 效果图