add fs to node code example

Example 1: fs writefile node

const fs = require('fs')

const content = 'Some content!'

fs.writeFile('/Users/joe/test.txt', content, err => {
  if (err) {
    console.error(err)
    return
  }
  //file written successfully
})

Example 2: fs create or edit file

//Edit file or creates if doesnt exist
 const fs = require('fs');
 fs.appendFile(‘<fileName>’,<content>,callbackFunction)