docs: add db save-password and create role to README command list

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: aprimakina

README.md

@@ -115,6 +115,8 @@ Tiger CLI provides the following commands:
   - `connection-string` - Get connection string for a service
   - `test-connection` - Test database connectivity
   - `schema` - Display database schema information (tables, views, indexes, functions, TimescaleDB hypertables, and more)
+  - `save-password` - Save a database password to configured password storage (keyring, pgpass, or none)
+  - `create role` - Create a new database role, with optional read-only enforcement, inherited grants (`--from`), and statement timeout
 - `tiger config` - Configuration management
   - `show` - Show current configuration
   - `set` - Set configuration value