Updates to Group Using Cloud-mode

Mixpanel's Director of Technology Partnerships submitted a ticket to Friends@segment:

We’ve received some feedback from a customer using Segment & Mixpanel for group analytics, how to improve (y)our docs. The issue is that our super properties don’t work when using Group Analytics in Cloud mode.

Would you be open to adding some language to this doc, under the "Group using Cloud-mode" section
https://segment.com/docs/connections/destinations/catalog/mixpanel/#group

"if you're using Cloud-mode you must explicitly include the grouping value as an event property on any event you wish to analyze with group analytics” (or something similar)

Author: segment-sv

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

@@ -148,6 +148,8 @@ You won't see server-side `traits` appear as super-properties on any events you
 
 For Mixpanel People, it's important to `identify` a user before you call `track`. A `track` without an `identify` won't create a user in Mixpanel People.
 
+if you're using Cloud-mode you must explicitly include the grouping value as an event property on any event you wish to analyze with Mixpanel's Group Analytics.
+
 ### Register Super Properties
 
 By default, each trait (i.e. properties in an `identify` call) is registered as a super property. This does not require passing a `userId` in the `identify` call. You can pass a `traits` object by itself and it will still register the traits as super properties.