Add package.json scripts ro run android and ios in template (#25618)
Add package.json scripts ro run android and ios in template (#25618)

Summary:
Currently users have to use the global `react-native` command or run `yarn react-native run-x` which isn't very nice.

This PR adds `android` and `ios` scripts to `package.json` so users can run `yarn android` or `yarn ios` directly.
Pull Request resolved: https://github.com/facebook/react-native/pull/25618

Differential Revision: D16223229

Pulled By: cpojer

fbshipit-source-id: 69b082760ff2ee31ab0406251f9a50339fd227bf

arthuralee/react-native,hammerandchisel/react-native,facebook/react-native,pandiaraj44/react-native,pandiaraj44/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponent/react-native,hammerandchisel/react-native,hoangpham95/react-native,pandiaraj44/react-native,myntra/react-native,janicduplessis/react-native,exponentjs/react-native,hoangpham95/react-native,javache/react-native,facebook/react-native,hoangpham95/react-native,javache/react-native,janicduplessis/react-native,hoangpham95/react-native,exponentjs/react-native,myntra/react-native,facebook/react-native,exponent/react-native,arthuralee/react-native,javache/react-native,hammerandchisel/react-native,pandiaraj44/react-native,janicduplessis/react-native,exponentjs/react-native,javache/react-native,exponent/react-native,janicduplessis/react-native,myntra/react-native,facebook/react-native,hoangpham95/react-native,hammerandchisel/react-native,javache/react-native,exponentjs/react-native,hoangpham95/react-native,myntra/react-native,exponentjs/react-native,exponent/react-native,hammerandchisel/react-native,myntra/react-native,pandiaraj44/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,facebook/react-native,hammerandchisel/react-native,exponentjs/react-native,javache/react-native,myntra/react-native,janicduplessis/react-native,facebook/react-native,exponentjs/react-native,javache/react-native,hammerandchisel/react-native,arthuralee/react-native,exponent/react-native,exponent/react-native,arthuralee/react-native,janicduplessis/react-native,hoangpham95/react-native,javache/react-native,arthuralee/react-native,myntra/react-native,exponent/react-native,myntra/react-native,janicduplessis/react-native,exponent/react-native,myntra/react-native,exponentjs/react-native,javache/react-native,hoangpham95/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native