updated readme with description of read-only user for database integration with home assistant

README.md

@@ -70,7 +70,66 @@ energy-consumption-ingester/
 
    # (Optional) verify new user and database creation
    \q
-   psql -U <DB_USER> -h <POSTGRES_HOST> -p <POSTGERS_PORT>
+   psql -U <DB_USER> -h <POSTGRES_HOST> -p <POSTGRES_PORT>
+   ```
+
+5. **OPTIONAL - Add read-only user to database:**
+
+   ```bash
+   # Connect to PostgreSQL as admin user
+   psql -U <POSTGRES_ADMIN> -h <POSTGRES_HOST> -p <POSTGRES_PORT> -d <DB_NAME>
+
+   # Create read-only user
+   CREATE USER <READONLY_USER> WITH PASSWORD '<READONLY_PASSWORD>';
+
+   # Grant connect privilege to the database
+   GRANT CONNECT ON DATABASE <DB_NAME> TO <READONLY_USER>;
+
+   # Grant usage on the schema (assuming default 'public' schema)
+   GRANT USAGE ON SCHEMA public TO <READONLY_USER>;
+
+   # Grant select privileges on all existing tables
+   GRANT SELECT ON ALL TABLES IN SCHEMA public TO <READONLY_USER>;
+
+   # Grant select privileges on all future tables (important for new tables)
+   ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO <READONLY_USER>;
+
+   # Grant usage on all existing sequences (needed for serial columns)
+   GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO <READONLY_USER>;
+
+   # Grant usage on all future sequences
+   ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT USAGE ON SEQUENCES TO <READONLY_USER>;
+
+   # Verify the read-only user can connect and query
+   \q
+   psql -U <READONLY_USER> -h <POSTGRES_HOST> -p <POSTGRES_PORT> -d <DB_NAME>
+   
+   # Test read access (should work)
+   SELECT COUNT(*) FROM metering_points;
+   SELECT COUNT(*) FROM consumption_readings;
+   
+   # Test write access (should fail)
+   INSERT INTO metering_points (metering_point_id) VALUES ('test'); -- Should get permission denied
+   ```
+
+   **For Home Assistant integration**, use these read-only credentials in your `configuration.yaml`:
+
+   ```yaml
+   # configuration.yaml
+   sensor:
+     - platform: sql
+       db_url: postgresql://<READONLY_USER>:<READONLY_PASSWORD>@<POSTGRES_HOST>:<POSTGRES_PORT>/<DB_NAME>
+       queries:
+         - name: "Latest Energy Reading"
+           query: >
+             SELECT 
+               consumption_kwh,
+               timestamp
+             FROM consumption_readings 
+             ORDER BY timestamp DESC 
+             LIMIT 1
+           column: consumption_kwh
+           unit_of_measurement: "kWh"
    ```
 
 ## Configuration