api docs: Add API changelog update for registration transfer.

api_docs/changelog.md

@@ -20,6 +20,15 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 10.0
 
+**Feature level 345**
+
+* `POST /remotes/server/register/transfer`,
+  `POST /remotes/server/register/verify_challenge`,
+  `POST /zulip-services/verify/{access_token}/`: Added new API
+  endpoints for transferring Zulip services registrations.
+* `POST /remotes/server/register`: Added new response format for
+  hostnames that are already registere.
+
 **Feature level 344**
 
 * `PATCH /realm`, [`GET /events`](/api/get-events),