readme: add pods example [skip ci]

README.md

@@ -33,6 +33,7 @@ just kaniko
 # start postgres.
 just dbstart
 
+# in another terminal, run the application.
 # make sure to supply real CONNSTRING values for production environment.
 podman run --rm -it -e PCMT_DBTYPE=postgres \
     -e PCMT_CONNSTRING="host=127.0.0.1 port=5432 sslmode=disable dbname=postgres password=postgres"
@@ -40,6 +41,39 @@ podman run --rm -it -e PCMT_DBTYPE=postgres \
     -config /etc/pcmt/config.dhall
 ```
 
+while the above is fine, running in *pods* is more close to a production
+setting (assuming rootless setup):
+```sh
+# create a pod.
+podman pod create --userns=keep-id -p3005:3000 --name pcmt
+
+# run a db in the pod.
+podman run --pod pcmt --replace -d --name "pcmt-pg" --rm \
+    -e POSTGRES_INITDB_ARGS="--auth-host=scram-sha-256 --auth-local=scram-sha-256" \
+    -e POSTGRES_PASSWORD=postgres -v $PWD/tmp/db:/var/lib/postgresql/data \
+    docker.io/library/postgres:15.2-alpine3.17
+
+# run the application in the pod (assuming that you have built it as in the
+# previous example). do note that we're connecting to the db using its
+# container name, while localhost would also work. inside the pod, every
+# container is reachable on localhost.
+podman run --pod pcmt --replace --name pcmt-og -d --rm \
+    -e PCMT_LIVE=False \
+    -e PCMT_DBTYPE="postgres" \
+    -e PCMT_CONNSTRING="host=pcmt-pg port=5432 sslmode=disable user=postgres dbname=postgres password=postgres" \
+    -v $PWD/config.dhall:/config.dhall:ro \
+    docker.io/immawanderer/pcmt:testbuild -config /config.dhall
+
+# also, if we try to connect to the db from the host we get an error (unless
+there is another database running on localhost already, such as the one from
+the previous example).
+
+curl localhost:5432
+--> curl: (7) Failed to connect to localhost port 5432 after 0 ms: Couldn't connect to server
+
+# that is because the database port has not been exposed from the pod (recall
+the pod creation command).
+```
 
 #### Custom config