Add Trino configuration docs

- with process forwarding config only for now

docs/installation.md

@@ -89,6 +89,32 @@ various cloud platforms, such as Amazon EKS also work. However Amazon Athena
 does not work since it uses alternative, custom protocols and lacks the concept
 of individual clusters.
 
+### Trino configuration
+
+From a users perspective Trino Gateway acts as a transparent proxy for one 
+or more Trino clusters. The following Trino configuration tips should be 
+taken into account for all clusters behind the Trino Gateway.
+
+Process forwarding must be enabled:
+
+```commandline
+http-server.process-forwarded=true
+```
+
+Without this setting, first requests go from the user to Trino Gateway and then
+to Trino correctly. However, the URL for subsequent next URIs for more results
+in a query provided by Trino is then using the local URL of the Trino cluster,
+and not the URL of the Trino Gateway. This circumvents the Trino Gateway for all
+these requests, and is contrary to the purpose of using the Trino Gateway. In
+scenarios, where the local URL of the Trino cluster is private to the Trino
+cluster on the DNS/network level, these following calls might not work at all
+for users.
+
+This setting is also required for Trino to authenticate in the case TLS is 
+terminated at the Trino Gateway. Normally it refuses to authenticate plain HTTP 
+requests, but if `http-server.process-forwarded=true` it authenticates over 
+HTTP if the request includes `X-Forwarded-Proto: HTTPS`.
+
 ## Configuration
 
 After downloading or building the JAR, rename it to `gateway-ha.jar`,