docs(README.md): List run_manifest_validation

Author: dimovpetar

README.md

@@ -31,6 +31,7 @@ The UI5 [Model Context Protocol](https://modelcontextprotocol.io/) server offers
 - `run_ui5_linter`: Integrates with [`@ui5/linter`](https://github.com/UI5/linter) to analyze and report issues in UI5 code.
 - `get_integration_cards_guidelines`: Provides access to UI Integration Cards development best practices.
 - `create_integration_card`: Scaffolds a new UI Integration Card.
+- `run_manifest_validation`: Validates the manifest against the UI5 Manifest schema.
 
 ## Requirements