📙 masterKey needed in push notifications JS Guide

[TomWFox]

Link to section: https://docs.parseplatform.org/js/guide/#using-channels

What is the issue? The code snippets & explanation don't mention that the masterKey is required to send push notifications.

Can you propose a solution? Adding a not about the need to add {useMasterKey: true}. Although the master key should only be used for the JS SDK when used in cloud code - so that should be considered.