docs(README): add SonarCloud badge for code quality monitoring

Author: mrz1836

README.md

@@ -21,6 +21,9 @@
         </a><br/>
 		    <a href="https://github.com/bsv-blockchain/go-overlay-discovery-services/actions">
           <img src="https://github.com/bsv-blockchain/go-overlay-discovery-services/actions/workflows/codeql-analysis.yml/badge.svg?style=flat" alt="CodeQL">
+        </a><br/>
+        <a href="https://sonarcloud.io/project/overview?id=bsv-blockchain_go-overlay-discovery-services">
+          <img src="https://sonarcloud.io/api/project_badges/measure?project=bsv-blockchain_go-overlay-discovery-services&metric=alert_status&style-flat" alt="SonarCloud">
         </a>
       </td>
       <td valign="top" align="left">