modify README

add Installation

README.md

@@ -1,13 +1,19 @@
 # Regexp Rename - Sketch Plugin
 
-You can change the layer name by Regexp in Sketch 3.
+This plugin can rename layer by Regexp in Sketch 3.
 
 ## Usage
 
 1. Select Layer(s).
 1. Choose **Plugins › Regexp Rename** (shortcut: `shift` + `ctrl` + `x`).
 1. Enter 'Find What:' and 'Replace With:' string, select Regexp flags.
 
+## Installation
+
+You can find this plugin in "[Sketch ToolBox.app](http://sketchtoolbox.com/)". Type "regexp" on the search box, then you click "install" button.
+
+Or, [Download the plugin zip](https://github.com/littlebusters/Regexp-Rename/archive/master.zip) and unzip. You Choose **Plugins › Reveal Plugins Folder...** in Sketch.app. Put the unziped fonlder to the Plugins folder. 
+
 ## License
 
 The MIT License (MIT)