Update GET top N api documentation

Signed-off-by: David Zane <[email protected]>

_observing-your-data/query-insights/top-n-queries.md

@@ -72,15 +72,13 @@ PUT _cluster/settings
 
 ## Monitoring the top N queries 
 
-You can use the Insights API endpoint to obtain the top N queries for all metric types:
+You can use the Insights API endpoint to obtain the top N queries. Specify the `type` parameter to get top N results for each metric type. Calling this API without `type` returns top N `latency` results by default.
 
 ```json
 GET /_insights/top_queries
 ```
 {% include copy-curl.html %}
 
-Specify a metric type to filter the response:
-
 ```json
 GET /_insights/top_queries?type=latency
 ```
@@ -96,6 +94,9 @@ GET /_insights/top_queries?type=memory
 ```
 {% include copy-curl.html %}
 
+If you are not seeing results, verify top N is enabled for the target metric type and ensure search requests were sent during the current `window_size`.
+{: .important}
+
 ## Exporting top N query data
 
 You can configure your desired exporter to export top N query data to different sinks, allowing for better monitoring and analysis of your OpenSearch queries. Currently, the following exporters are supported: