update README.md, template docker-compose.yaml and the documentation

Writerside/topics/database-configuration.md

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+# Database
+
+Database settings are configured in the `[database]` section of your `config.toml` file. MediaManager uses PostgreSQL as its database backend.
+
+## Database Settings (`[database]`)
+
+- `host`
+
+Hostname or IP of the PostgreSQL server. Default is `localhost`.
+
+- `port`
+
+Port number of the PostgreSQL server. Default is `5432`.
+
+- `user`
+
+Username for PostgreSQL connection. Default is `MediaManager`.
+
+- `password`
+
+Password for the PostgreSQL user. Default is `MediaManager`.
+
+- `dbname`
+
+Name of the PostgreSQL database. Default is `MediaManager`.
+
+## Example Configuration
+
+Here's a complete example of the database section in your `config.toml`:
+
+```toml
+[database]
+host = "db"
+port = 5432
+user = "MediaManager"
+password = "your_secure_password"
+dbname = "MediaManager"
+```
+
+<tip>
+    In docker-compose deployments the containers name is simultaneously its hostname, so you can use "db" or "postgres" as host.
+</tip>