Invalid code example in README

[Hiromu Asahina]

Hi, I found mismatch between an example in README and the actual code. The first example in README imports initializeApp, but it's actually initializeFirebaseApp [1].

const { initializeApp } = require('firestore-export-import')

// The above line should be 
const { initializeFirebaseApp } = require('firestore-export-import')

[1] https://github.com/dalenguyen/firestore-backup-restore/blob/dev/src/index.ts#L18