Update index-templates.asciidoc

Author: juliaElastic

docs/reference/indices/index-templates.asciidoc

@@ -70,6 +70,9 @@ ensures your template is applied instead of the built-in template for
 `logs-*-*`.
 
 - To avoid naming collisions with built-in and Fleet-managed index templates, avoid using `@` as part of the name of your own index templates.
+
+- Fleet uses index `fleet-synced-integrations` for a feature, avoid using this name to avoid naming collisions.
+
 ****
 
 [discrete]