Update README.md

Author: mugetsu

README.md

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 # COVID-19 Tracker 
-tracks COVID-19 around the world
+[Web App](https://covid-worldwide.herokuapp.com/) that tracks COVID-19 around the world
 
 ## API
 The API was provided by [ExpDev07/coronavirus-tracker-api](https://github.com/ExpDev07/coronavirus-tracker-api).