update db connection part in user docs

docs/user.md

@@ -43,13 +43,25 @@ $ kubectl get pods -w --show-labels
 
 ## Connect to PostgreSQL
 
-We can use the generated secret of the `postgres` robot user to connect to our `acid-minimal-cluster` master running in Minikube:
+With a `port-forward` on one of the database pods (e.g. the master) you can
+connect to the PostgreSQL database. Use labels to filter for the master pod of
+our test cluster.
+
+```bash
+# get name of master pod of acid-minimal-cluster
+export PGMASTER=$(kubectl get pods -o jsonpath={.items..metadata.name} -l application=spilo,version=acid-minimal-cluster,spilo-role=master)
+
+# set up port forward
+kubectl port-forward $PGMASTER 6432:5432
+```
+
+Open another CLI and connect to the database. Use the generated secret of the
+`postgres` robot user to connect to our `acid-minimal-cluster` master running
+in Minikube:
 
 ```bash
-$ export PGHOST=db_host
-$ export PGPORT=db_port
 $ export PGPASSWORD=$(kubectl get secret postgres.acid-minimal-cluster.credentials -o 'jsonpath={.data.password}' | base64 -d)
-$ psql -U postgres
+$ psql -U postgres -p 6432
 ```
 
 # Defining database roles in the operator