fix maven-xml 3 description

Author: hboutemy

README.md

@@ -2,9 +2,10 @@ Plexus-Xml
 ============
 
 [![Build Status](https://github.com/codehaus-plexus/plexus-xml/actions/workflows/maven.yml/badge.svg)](https://github.com/codehaus-plexus/plexus-xml/actions)
-[![Maven Central](https://img.shields.io/maven-central/v/org.codehaus.plexus/plexus-xml.svg?label=Maven%20Central)](https://search.maven.org/artifact/org.codehaus.plexus/plexus-xml)
+[![Maven Central](https://img.shields.io/maven-central/v/org.codehaus.plexus/plexus-xml.svg?label=Maven%20Central&versionPrefix=3.)](https://search.maven.org/artifact/org.codehaus.plexus/plexus-xml)
 
-This library consists of XML classes (`org.codehaus.plexus.util.xml`, and `ReaderFactory`/`WriterFactory` moved from `org.codehaus.plexus.util`) that have been extracted from [`plexus-utils`](https://github.com/codehaus-plexus/plexus-utils/) 4.
+This library consists of XML classes (`org.codehaus.plexus.util.xml`) that have been extracted from [`plexus-utils`](https://github.com/codehaus-plexus/plexus-utils/) 3:
+> `plexus-utils` 3 = `plexus-utils` 4 + `plexus-xml` 3.
 
 For publishing [the site](https://codehaus-plexus.github.io/plexus-xml/) do the following: