add informatino about required synapse listeners

Author: fkwp

docs/self-hosting.md

@@ -63,6 +63,11 @@ rc_delayed_event_mgmt:
   burst_count: 20
 ```
 
+As a prerequisites for the
+[Matrix Livekit JWT auth service](https://github.com/element-hq/lk-jwt-service)
+make sure that your Synapse server has either a `federation` or `openid`
+[listener configured](https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html#listeners).
+
 ### MatrixRTC Backend
 
 In order to **guarantee smooth operation** of Element Call MatrixRTC backend is