Add Focus (Pomodoro App)

Focus is a well-designed productivity app based on the pomodoro technique.

https://masterbuilders.io

README.md

@@ -517,6 +517,7 @@ It is a free and open source software.[![Open-Source Software][OSS Icon]](https:
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+* [Focus](https://masterbuilders.io) - A beautiful pomodoro-based time manager. [![App Store][app-store Icon]](https://itunes.apple.com/us/app/focus-productivity-timer/id777233759?mt=12)
 
 ### Productivity
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