[update] readme

Author: hiyorin

Assets/Plugins/MemoryInfoPlugin

@@ -2,8 +2,22 @@
 A set of tools for Unity to allow handling memory info for Android and iOS.
 
 # Install
+## unitypackage
 MemoryInfoPlugin-for-Unity.unitypackage
 
+## package manager
+Specify repository URL git://github.com/hiyorin/upm.MemoryInfoPlugin-for-Unity.git with key com.hiyorin.memoryinfo into Packages/manifest.json like below.
+```javascript
+{
+  "dependencies": {
+    // ...
+    "com.hiyorin.memoryinfo": "git://github.com/hiyorin/upm.MemoryInfoPlugin-for-Unity.git",
+    // ...
+  }
+}
+```
+
+
 # Usage
 ```cs
 using MemoryInfo;