Add more details on Networking page

[mborgerson]

Currently the networking page only describes the possible use cases, and some instructions for setting up tap networking. I think users would benefit from having some extra details added to this page before being directed to the official QEMU docs (which could be overwhelming for newcomers), e.g.:

• A note about EEPROM/MAC addresses (two instances of XQEMU cannot have the same MAC address and talk to eachother)
• How to set up a simple XQEMU<->XQEMU socket based network
• How to forward ports when using NAT