Document how getWebServiceHost and getWebServicePort have to be configured

When JBPM 4.1 is deployed on Tomcat, the "formUrl" attribute of process definitions is always "http://localhost:8080/...".

The problem is in org.jbpm.integration.spi.mgmt.ServerConfigFactory which create an org.jbpm.integration.spi.mgmt.DefaultServerConfig for Tomcat. And DefaultServerConfig's methods getWebServiceHost and getWebServicePort always return "localhost" and "8080".