Document spaces option for writeJson & outputJson

[sidvishnoi]

It would be nice if there is an option for pretty-printing JSON while writing file.

[RyanZim]

There is an option; it's called spaces.

fs.writeJson(file, {some: 'data'}, {spaces: 2})
.then(() => {
  console.log('success!')
})
.catch(err => {
  console.error(err)
})

This should be documented.