docs(readme): add SonarCloud quality gate badge.

Author: ybeshkarov

README.md

@@ -1,4 +1,5 @@
 [![pub package](https://img.shields.io/pub/v/smf_flutter_cli.svg)](https://pub.dev/packages/smf_flutter_cli)
+[![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=saymyframe_smf_flutter_cli&metric=alert_status)](https://sonarcloud.io/summary/new_code?id=saymyframe_smf_flutter_cli)
 [![status: preview](https://img.shields.io/badge/status-preview-blue.svg)](https://github.com/saymyframe/smf_flutter_cli/issues)
 [![license](https://img.shields.io/badge/license-Apache%202.0-blue.svg)](LICENSE)
 [![Join us on Discord](https://img.shields.io/badge/Join%20us-Discord-5865F2?logo=discord&logoColor=white)](https://saymyframe.com/discord)