improve README: note on how to test staged Tomcat maven artifacts
improve README: note on how to test staged Tomcat maven artifacts

git-svn-id: 127192e8212bb0c5b19f2c3aa333cc66dfed8a45@1290880 13f79535-47bb-0310-9956-ffa450edef68

markmclaren/tomcat-maven-plugin,karthikjaps/Tomcat,markmclaren/tomcat-maven-plugin,bmeriaux/tomcat-maven-plugin,karthikjaps/Tomcat,markmclaren/tomcat-maven-plugin,bmeriaux/tomcat-maven-plugin,apache/tomcat-maven-plugin,bmeriaux/tomcat-maven-plugin,codelibs/tomcat-maven-plugin,karthikjaps/Tomcat,codelibs/tomcat-maven-plugin,apache/tomcat-maven-plugin,apache/tomcat-maven-plugin