Add Trino configuration docs

- with process forwarding config only for now

docs/installation.md

@@ -89,6 +89,27 @@ 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 scenario, 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.
+
 ## Configuration
 
 After downloading or building the JAR, rename it to `gateway-ha.jar`,