[doc] Add Maven badge to README.md

Author: adamretter

README.md

@@ -1,6 +1,9 @@
 Corpus Query Language Parser
 ============================
-[![Build Status](https://github.com/exquery/corpusql-parser/actions/workflows/ci.yml/badge.svg)](https://github.com/exquery/corpusql-parser/actions/workflows/ci.yml) [![Java 8+](https://img.shields.io/badge/java-8+-4c7e9f.svg)](http://java.oracle.com) [![License](https://img.shields.io/badge/license-BSD-blue.svg)](http://opensource.org/licenses/BSD-3-Clause)
+[![Build Status](https://github.com/exquery/corpusql-parser/actions/workflows/ci.yml/badge.svg)](https://github.com/exquery/corpusql-parser/actions/workflows/ci.yml)
+[![Java 8+](https://img.shields.io/badge/java-8+-4c7e9f.svg)](http://java.oracle.com)
+[![License](https://img.shields.io/badge/license-BSD-blue.svg)](http://opensource.org/licenses/BSD-3-Clause)
+[![Maven Central](https://img.shields.io/maven-central/v/com.evolvedbinary.cql/corpusql-parser?logo=apachemaven&label=maven+central&color=green)](https://search.maven.org/search?q=g:com.evolvedbinary.cql)
 
 This library implements a Corpus Query Language Parser in Java 1.8, using [Antlr v4](http://www.antlr.org/).