Update images in readme

Author: thomasnordquist

Readme.md

@@ -8,7 +8,7 @@
 
 |   |   |   |
 |:---:|:---:|:---:|
-|[![screen1_small](https://user-images.githubusercontent.com/7721625/53954800-84b34c00-40d7-11e9-842d-bf655c569600.jpg)](https://user-images.githubusercontent.com/7721625/53954364-52551f00-40d6-11e9-93cf-d5a9601897ea.png)|[![screen2_small](https://user-images.githubusercontent.com/7721625/53954801-84b34c00-40d7-11e9-913a-42572e675620.jpg)](https://user-images.githubusercontent.com/7721625/53954365-52551f00-40d6-11e9-823f-afd66f19ed01.png)|[![screen3_small](https://user-images.githubusercontent.com/7721625/53954802-854be280-40d7-11e9-973c-08f23c8dbf89.jpg)](https://user-images.githubusercontent.com/7721625/53954366-52551f00-40d6-11e9-9738-74db830d03ac.png)|
+|[![screen_composite](https://mqtt-explorer.com/img/screen-composite_small.png)](https://mqtt-explorer.com/img/screen-composite.png)|[![screen2_small](https://mqtt-explorer.com/img/screen2_small.png)](https://mqtt-explorer.com/img/screen2.png)|[![screen3_small](https://mqtt-explorer.com/img/screen3_small.png)](https://mqtt-explorer.com/img/screen3.png)|
 
 # The App has moved to [mqtt-explorer.com](https://mqtt-explorer.com)
 MQTT Explorer is a comprehensive and easy-to-use MQTT Client.