Explain matrix_postgres_container_postgres_bind_port a little more

Previously, it only mentioned exposing for psql-usage purposes.

Realistically, it can be used for much more. Especially given that
psql can be easily accessed via our matrix-postgres-cli script,
without exposing the container port.

roles/matrix-postgres/defaults/main.yml

@@ -17,7 +17,7 @@ matrix_postgres_docker_image_latest: "{{ matrix_postgres_docker_image_v11 }}"
 matrix_postgres_container_extra_arguments: []
 
 # Controls whether the matrix-postgres container exposes a port (tcp/5432 in the
-# container) that can be used to access the database with psql.
+# container) that can be used to access the database from outside the container (e.g. with psql)
 #
 # psql postgresql://username:password@localhost:<port>/database_name
 #