Update SSO guide

Added information from #1017

guides/SSO.md

@@ -46,3 +46,6 @@ docker run -p 8080:8080 -v `pwd`/cert:/opt/cert -e AUTH_ENABLED=true \
   -e SPRING_SECURITY_OAUTH2_CLIENT_PROVIDER_AUTH0_ISSUER_URI=https://dev-a63ggcut.auth0.com/ \
 provectuslabs/kafka-ui:0.1.0
 ```
+
+#### Step 4 (optional)
+If you're using load balancer/proxy and use HTTP between the proxy and the app, you might wanna set `SERVER_USEFORWARDHEADERS` to true as well, for more info refer to [this issue](https://github.com/provectus/kafka-ui/issues/1017).