added info on how to publish site

Author: hboutemy

README.md

@@ -2,5 +2,12 @@ Plexus-Utils
 ============
 
 [![Build Status](https://travis-ci.org/codehaus-plexus/plexus-utils.svg?branch=master)](https://travis-ci.org/codehaus-plexus/plexus-utils)
+[![Maven Central](https://img.shields.io/maven-central/v/org.codehaus.plexus/plexus-utils.svg?label=Maven%20Central)](http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.codehaus.plexus%22%20a%3A%plexus-utils%22)
 
 The current master is now at https://github.com/codehaus-plexus/plexus-utils
+
+For publishing the site do the following:
+
+```
+mvn -Preporting verify site site:stage scm-publish:publish-scm
+```