Update README.md (#1169)

Author: toolshref-tools

README.md

@@ -214,6 +214,7 @@ _Tools that provide metrics and quality measurements._
 - [SonarJava](https://github.com/SonarSource/sonar-java) - Static analyzer for SonarQube & SonarLint. (LGPL-3.0-only)
 - [Spoon](https://github.com/INRIA/spoon) - Library for analyzing and transforming Java source code.
 - [Spotbugs](https://github.com/spotbugs/spotbugs) - Static analysis of bytecode to find potential bugs. (LGPL-2.1-only)
+- [ToolsHref](https://toolshref.com) - Online Java code analyzer and JSON-to-Mermaid visualization tool.
 
 ### Code Coverage