Improve documentation for using Change Events & Listeners

In Change Event section, we do state "The live query starts immediately and changes are posted asynchronously." However, we do not explicitly state that when the observer is added, the query is going to be executed first - and then it will be watching for changes. This may result in developers creating a separate query call first, then adding the observable (which results in the second query call), which under certain conditions can cause thread locking.

It would be great if we can explain how to use these asynchronous change listeners, and why these should be performed asynchronously. I'm sure the Mobile Engineering team can assist with this.