Refer to Zulip import from Rocket.Chat docs

docs/upgrading.rst

@@ -96,20 +96,10 @@ renamed from ``oas`` to ``stackspin``. You can choose from these options:
 Rocket.Chat
 ~~~~~~~~~~~
 
-It is possible to back-up and restore Rocket.Chat, but you have to do it
-manually. Before you run the ``rename-to-stackspin.sh`` script, you need to run
-a ``mongodump`` of the database inside the pod. After everything is done and
-you have re-installed Rocket.Chat, you need to restore the mongodump with
-``mongorestore``:
-
-
-.. code:: bash
-
-   # These commands need to be run *inside* the rocketchat-mongodb pod:
-   # To dump:
-   mongodump --db rocketchat  <backup_dir> -u root --authenticationDatabase admin
-   # To restore:
-   mongorestore --db rocketchat  <backup_dir>/backup/rocketchat/rocketchat -u root --authenticationDatabase admin
+We replaced Rocket.Chat with `Zulip <https://zulip.com>`__ in this release.
+If you want to migrate your Rocket.Chat data to your new Zulip installation
+please refer to
+`Import from Rocket.Chat https://api.zulip.com/help/import-from-rocketchat`__.
 
 Monitoring
 ~~~~~~~~~~