add install info

Author: waderwu

README.md

@@ -8,6 +8,9 @@
 # Datalog Plugin for the IntelliJ Platform
 For a list of changes in the newest version, please refer to the [changelog](./CHANGELOG.md).
 
+## 安装
+目前只支持离线安装，安装包从[release](https://github.com/BytecodeDL/intellij-datalog/releases)下载
+
 ## 改进
 1. 增加了multi head的支持
 2. 增加了ByteCodeDL用到的一些语法比如`#if` `#paragma`等