Update README.md

Author: SergySanJj

README.md

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 # SmartTimer
 ![alt text](https://github.com/secondYearProjects/SmartTimer/blob/master/SmartTimer/icons/ST-main-icon64.png)
-Manage your timers and alarms easily
+## Manage your timers and alarms easily
 
+#### Tested on Windows 8.1, Windows 10, Ubuntu 18.04
+
+## Screenshots:
 ![alt text](https://github.com/secondYearProjects/SmartTimer/blob/master/screenshots/timer.png)
 ![alt text](https://github.com/secondYearProjects/SmartTimer/blob/master/screenshots/alarm.png)
+
 ![alt text](https://github.com/secondYearProjects/SmartTimer/blob/master/screenshots/settings.png)
+
 ![alt text](https://github.com/secondYearProjects/SmartTimer/blob/master/screenshots/global.png)