Update README.md

Author: xenirio

README.md

@@ -1,6 +1,8 @@
 # Electron ViewerJS
 The PDF/ODT/ODP embedded viewer based on ViewerJS for Electron.
 
+![screen-shot-1](https://user-images.githubusercontent.com/241133/71978767-ba244b00-324e-11ea-8d77-ac934f3ef61a.png)
+
 ## Installation
 ```bash
 $ npm i --save electron-viewerjs
@@ -53,4 +55,4 @@ viewer.new(ctx); //No need to put path here.
 let ctx = document.getElementById('sample-viewer-1');
 let preview = viewer.new(ctx);
 preview.loadSync('./sample-odt-doc.odt'); //Load ODT document file after initialized.
-```
+```