reword/reorg/simplify based on recent feedback.

 - don't worry about how multiple IP addresses map
 - simplify the description of why you might use an IP address in <virtualhost
 - move the note below the last paragraph



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1628690 13f79535-47bb-0310-9956-ffa450edef68