link to both context and event in depr notice as per review

api/client-server/old_sync.yaml

@@ -407,7 +407,8 @@ paths:
         retrieve this event e.g. by being a member in the room for this event.
 
         This endpoint was deprecated in r0 of this specification. Clients
-        should instead call the |/rooms/{roomId}/event/{eventId}|_ API.
+        should instead call the |/rooms/{roomId}/event/{eventId}|_ API
+        or the |/rooms/{roomId}/context/{eventId}|_ API.
       operationId: getOneEvent
       security:
         - accessToken: []