Add messaging to clarify current 1,000 device audience limit

[patniko]

Currently, App Center allows you to create an Audience of any size, but will only send notifications to the first 1,000 devices in the audience (skipping the remainder). To make this more clear for users, we updated the documentation to clearly state the limitation and describe App Center's behavior when you exceed the limit.

The next step is to update the App Center Push UI so it displays a warning when an audience exceeds the limit. This UI change will affect the Audience pages, but also places where you're sending a notification to an audience.

[patniko]

This was shipped today.