docs: add screenshot

Author: treetips

README.md

@@ -8,6 +8,16 @@ By VSCode and prettier and TSLint, realtime code format and realtime sentence st
 
 VSCode と prettier と TSLint によって、リアルタイムに整形と構文チェックと未使用 import の整理が行われます。
 
+## Screenshot
+
+### For desktop
+
+![For desktop](https://user-images.githubusercontent.com/12574048/46964420-f9fb9180-d0e2-11e8-9c05-e1594c533947.png)
+
+### For mobile
+
+![For mobile](https://user-images.githubusercontent.com/12574048/46964454-126bac00-d0e3-11e8-8bdc-ebf47c907ed1.png)
+
 ## Features
 
 - [Google App Engine Node.js Standard Environment](https://cloud.google.com/appengine/docs/standard/nodejs/)