Investigate how to use Metro caching

[mrtnzlml]

• https://facebook.github.io/metro/docs/en/caching
• https://facebook.github.io/react-native/docs/next/performance.html#ram-bundles-inline-requires

[mrtnzlml]

File metro.config.js (in the project root):

// @flow

const path = require('path');
const { FileStore } = require('metro-cache');

module.exports = {
  cacheStores: [
    new FileStore({
      root: path.join(__dirname, 'metro-cache'),
    }),
  ],
};