Merge pull request #5644 from segmentio/joeynmq-patch-6

Add note about sending Track events with a custom Group Key to Mixpanel

Author: stayseesong

src/connections/destinations/catalog/actions-mixpanel/index.md

@@ -133,3 +133,8 @@ If you want to confirm, you can configure the new destination to point to a diff
 
 If the Mixpanel (Actions) destination uses $group_id as the group key, ensure that the mappings handling your `track` events have the field for **Group ID** mapped to a valid value. By default, this field maps to the event variable `context.groupId`.
 
+To send Track events with a custom Group Key, include the key as a property of Track events. For example:
+```js
+analytics.track('Example Event', { custom_group_key : 'group1' });
+```
+