Clarified documentation on postgresql

docs/deployment/postgresql.md

@@ -9,18 +9,27 @@ order: 13
 
 The FROST-Server needs a database to store its data. Currently only [PostgreSQL](https://www.postgresql.org/) with the [PostGIS](https://postgis.net/) extensions is supported.
 
+
 ## Database installation
 
 1. create PostgreSQL database for the data
 2. install the postgis extensions in this database (`CREATE EXTENSION postgis;`)
 3. Optional: If you want to use UUIDs as entity ids, you need the uuid-ossp extension (`CREATE EXTENSION "uuid-ossp";`)
 
-## Database configuration
 
-The HTTP and all-in-one MQTTP packages use JNDI to get a database resource from Tomcat or Wildfly. You have to configure
-a resource in Tomcat/Wildfly, and then tell the FROST-Server what name you gave this resource.
+## Database Connection in FROST
+
+### Tomcat / Wildfly
+
+When FROST-Server is deployed directly on Tomcat or Wildfly, the HTTP and all-in-one MQTTP packages use JNDI to get a database resource.
+You have to configure a resource in Tomcat/Wildfly, and then tell the FROST-Server what name you gave this resource.
 The default name is `jdbc/sensorThings`.
 
+### Containers
+
+When deploying FROST-Server using containers, the database connection details are configured using environment variables.
+The relevant variables are: `persistence.db.url`, `persistence.db.username` and `persistence.db.password`.
+
 
 ## Database initialisation or upgrade