api-docs: Expands API changelog feature level 134 entry.

Expands API changelog feature level 134 entry and adds the related
Changes notes to the events documentation for the updates made in
commit f4fcedd: "stream op: create" and "subscription op: peer_add"
events being sent when a private stream is made public.

Those changes were made after the feature level 133 updates, but
before the feature level 134 updates, which is why 134 is the
feature level for the change that is documented for clients.

api_docs/changelog.md

@@ -702,6 +702,9 @@ user's profile.
   to the response. This generalizes and replaces the previous
   `muted_topics` array, which will no longer be sent if `user_topic`
   is included in `fetch_event_types`.
+* [`GET /events`](/api/get-events): When private streams are made
+  public, `stream` events for `op: "create"` and `subscription` events
+  for `op: "peer_add"` are now sent to clients.
 
 **Feature level 133**
 

zerver/openapi/zulip.yaml

@@ -776,6 +776,9 @@ paths:
                                 sent when a user gained access to a stream due to their [role
                                 changing](/help/roles-and-permissions).
 
+                                Prior to Zulip 6.0 (feature level 134), this event was not sent when a
+                                private stream was made public.
+
                                 In Zulip 4.0 (feature level 35), the singular `user_id` and `stream_id`
                                 integers included in this event were replaced with plural `user_ids` and
                                 `stream_ids` integer arrays.
@@ -1191,6 +1194,9 @@ paths:
                                 Prior to Zulip 8.0 (feature level 192), this event was not sent
                                 when guest users gained access to a public stream by being
                                 subscribed.
+
+                                Prior to Zulip 6.0 (feature level 134), this event was not sent
+                                when a private stream was made public.
                               properties:
                                 id:
                                   $ref: "#/components/schemas/EventIdSchema"