fix confusing remark about NSS divergence from the spec

Author: michielbdejong

api-websockets.md

@@ -49,8 +49,7 @@ space and the URI of the resource that has changed:
 pub https://example.org/data/test
 ```
 
-Some implementations also support using IRIs that are relative to the host,
-e.g. `/data/test` instead of `https://example.org/data/test`.
+Only absolute URIs should be used in both the `sub` and the `pub` message.
 
 Subscribing to a container can also be really useful, since all CRUD operations
 (POST, PUT, PATCH, DELETE) performed on resources of that container will trigger