README.md: add screenshot [ci skip]

Author: yuk7

README.md

@@ -2,6 +2,7 @@
 CentOS on WSL (Windows 10 FCU or later)
 based on [wsldl](https://github.com/yuk7/wsldl)
 
+![screenshot](https://raw.githubusercontent.com/wiki/yuk7/wsldl/img/Cent_Arch_Alpine.png)
 [![Build Status](https://img.shields.io/travis/yuk7/CentWSL.svg?style=flat-square)](https://travis-ci.org/yuk7/CentWSL)
 [![Github All Releases](https://img.shields.io/github/downloads/yuk7/CentWSL/total.svg?style=flat-square)](https://github.com/yuk7/CentWSL/releases/latest)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square)](http://makeapullrequest.com)