Update the network ports page in the docs to add more details about ports that need to be opened for XDCR

Add a section to the Network Port page http://www.couchbase.com/docs/couchbase-manual-2.0/couchbase-network-ports.html for XDCR to illustrate the following.

Replication occurs between the individual nodes within each cluster. If you are communicating with a destination cluster over a dedicated connection or the Internet you should ensure that all the nodes in the destination and source clusters can communicate with each other over ports 8091 and 8092.

This is where people will look (a customer just looked at this as well) and not find the information.