Add API doc

README.md

@@ -26,4 +26,12 @@ One simple command could bring the Jenkins wechat backend up:
 
 `docker run -t -p 12345:8080 -v /var/wechat/config:/config surenpi/jenkins-wechat`
 
-docker run -t -p 45678:18080 -v /var/wechat/config:/config surenpi/jenkins-wechat:dev--LinuxSuRen-gmail.com
\ No newline at end of file
+docker run -t -p 45678:18080 -v /var/wechat/config:/config surenpi/jenkins-wechat:dev--LinuxSuRen-gmail.com
+
+## API
+
+Below are the APIs of WeChat bot:
+
+| Path | Description |
+|---|---|
+| GET `/medias` | Returns the media file list |