Added screenshot to README

Author: issmirnov

Diff for: README.md

@@ -8,6 +8,6 @@ Official docs: https://www.dokuwiki.org/plugin:diffpreview
 
 This plugin adds the option to view a diff of your changes, which can be useful if you don't want to view a full preview.
 
-
+![screenshot](screenshot1.png)
 
 **NOTE: I am not the original author, merely the current maintainer who accepts reasonable pull requests.**