Add screenshot

Fixes: #125

Author: johanmalm

README.md

@@ -4,7 +4,7 @@
 
 This is a GUI 'Settings' application for labwc.
 
-<img src="https://private-user-images.githubusercontent.com/6955353/456192696-a8070566-5676-4932-a187-9e984943dfdd.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.kjAiUZyN771SQ3T7_MNY2rTFPFzV9ABiBzImu9MCyfI"/>
+<img src="data/screenshot.png"/>
 
 ### dependencies