Add an example QueryStats query

docs/changelog/6_x.rst

@@ -15,6 +15,8 @@ automatically suggested:
 Upgrading
 =========
 
+.. edb:collapsed::
+
 **Local instances**
 
 To upgrade a local project, first ensure that your CLI is up to date with
@@ -121,7 +123,24 @@ upgrade more frequently.
 Query performance observability
 -------------------------------
 
-We now store statistics about query performance.
+We now store statistics about query performance. These statistics are available
+in ``sys::QueryStats`` objects.
+
+.. code-block:: edgeql
+
+  select sys::QueryStats {
+    query,
+    queryType,
+    tag,
+    plans,
+    total_plan_time,
+    mean_plan_time,
+    calls,
+    total_exec_time,
+    mean_exec_time,
+  } filter .branch.name = sys::get_current_branch();
+
+More details to come in the reference documentation.
 
 ``ext::postgis``
 ----------------