Move audience key warning

Author: pwseg

src/engage/audiences/index.md

@@ -26,6 +26,9 @@ You can build an Audience from existing events, traits, computed traits, or othe
 > warning ""
 > Editing an audience before the initial backfill is complete can create technical errors.
 
+> warning "Audience Keys"
+> Avoid using the same Audience key twice, even if you've deleted the original Audience.
+
 ### Events
 
 You can build an Audience from any events that are connected to Engage, including [Track](/docs/connections/spec/track), [Page](/docs/connections/spec/page), and [Screen](/docs/connections/spec/screen) calls. You can use the `property` button to refine the audience on specific event properties, as well. 
@@ -85,7 +88,6 @@ If you have a B2B business, you might want to build an Audience of accounts. You
 See [Account-level Audiences](/docs/engage/audiences/account-audiences) for more information.
 
 
-
 ## Send Audiences to Destinations
 With the help of Sources and Destinations in Segment's catalog, you can create and send Audiences and computed traits to third-party services.