docs: add database support section with CI badges for various database systems. (#63)

Author: terabytesoftw

README.md

@@ -277,6 +277,13 @@ For detailed configuration options and advanced usage.
 - 💡 [Usage Examples](docs/examples.md)
 - 🧪 [Testing Guide](docs/testing.md)
 
+## Database support
+
+[![Microsoft SQL Server](https://img.shields.io/badge/Microsoft%20SQL%20Server-CC2927?style=for-the-badge&logo=microsoft%20sql%20server&logoColor=white)](https://github.com/yii2-extensions/nested-sets-behavior/actions/workflows/build-mssql.yml)
+[![MySQL](https://img.shields.io/badge/mysql-4479A1.svg?style=for-the-badge&logo=mysql&logoColor=white)](https://github.com/yii2-extensions/nested-sets-behavior/actions/workflows/build-mysql.yml)
+[![Oracle](https://img.shields.io/badge/Oracle-F80000?style=for-the-badge&logo=oracle&logoColor=white)](https://github.com/yii2-extensions/nested-sets-behavior/actions/workflows/build-oracle.yml)
+[![PostgreSQL](https://img.shields.io/badge/postgresql-4169e1?style=for-the-badge&logo=postgresql&logoColor=white)](https://github.com/yii2-extensions/nested-sets-behavior/actions/workflows/build-pgsql.yml)
+[![SQLite](https://img.shields.io/badge/sqlite-003B57.svg?style=for-the-badge&logo=sqlite&logoColor=white)](https://github.com/yii2-extensions/nested-sets-behavior/actions/workflows/build.yml)
 
 ## Quality code