Add Github topics to repo

[emanuelb]

improve project discoverability by adding github topics, see: https://help.github.com/en/github/administering-a-repository/classifying-your-repository-with-topics

covid-19 used topics are: https://github.com/topics/covid https://github.com/topics/covid-virus https://github.com/topics/covid19 https://github.com/topics/covid-19 https://github.com/topics/corona https://github.com/topics/coronavirus

related mobile topics are: https://github.com/topics/react-native

[kaplanlior]

Thanks. Added covid-19 and coronavirus which seem the two most popular.