added managed-stats endpoint log entry

Author: hzoppetti

src/content/changelog/2019-10-07-api.md

@@ -36,6 +36,8 @@ Some heuristics for which heading to put API reference updates under:
 * A `linode_reboot` Event action can now generate a `secondary_entity` object. A `secondary_entity` object displays information about an additional entity that is related to the Event.
     * Use the Accounts collection to List Events [GET /account/events](/api/v4/account-events) or to View an Event [GET /account/events/{eventId}](/api/v4/account-events-event-id).
 
+* The List Managed Stats endpoint [GET managed/stats](/api/v4/managed-stats) returns a list of Managed Stats on your account in the form of y and x graph data points. These stats reflect the last 24 hours of combined usage for `cpu`, `disk`, `swap`, `network in`, and `network out`.
+
 ### Changed
 
 ### Fixed