Add to documentation that liveRegion should be set up before adding text

[Karl Groves]

Clarify the existing documentation by removing the text from the example.

Create another example that shows adding text.

The reason why this is important is that (in practice) screen readers don't announce content when it is added at the same time as the creation of the live region

[Karl Groves]

Closing this as a non-issue. Modifying the plugin to work around this issue.